Three weeks ago, all the students at my university were gathered in the hall of the campus. Three weeks ago, all the students at my university were gathered in the hall of the campus.

Continuous sounds better here to describe an ongoing situation. To me, using simple past makes it sound like the students were gathering to attend a specific event because it focuses on the action more than the state.

Three weeks ago, all the students at my university gathered in the hall of the campus. Three weeks ago, all the students at my university gathered in the hall of the campus.

"Hall of the campus" is a bit unclear – it's not a phrase we generally use in English, but I'm not quite sure what you mean, so I don't know what I'd suggest.

They were whispereding to each other that they saw a beautiful new transfer student who was joining the art major inat our university. They were whispering to each other that they saw a beautiful new transfer student who was joining the art major at our university.

Without "who was" it implies they saw the act of her joining the art major, which isn't really possible

Her name iwas Alana. Her name was Alana.

Because this story is written in past tense, this must match that

That girl looked reallvery kind, humble, and polite. That girl looked very kind, humble, and polite.

That girlShe looked really kind, humble, and polite. She looked really kind, humble, and polite.

Her blue eyes were so pretty, and her smile was alluring. Her blue eyes were so pretty, and her smile was alluring.

She was the kind of person that would beas adored by everybody who noticed her. She was the kind of person that was adored by everybody who noticed her.

When I tried to move my lips to speak to her, a strange, hoarse voice of hers filled my ears, “You missed Luna? When I tried to move my lips to speak to her, a strange, hoarse voice filled my ears, “You miss Luna?

"a voice of hers" sounds odd because people only have one voice. It is already implied that the voice belongs to Alana

When I tried to move my lips to speak to her, her a strange hoarse voice of hers filled my ears,: “You missed Luna? When I tried to move my lips to speak to her, her a strange hoarse voice filled my ears: “You missed Luna?

I promise I will take you there… hihihiehehe…” I promise I will take you there… hehehe…”

I promise I will take you there… hihihiehehe…” I promise I will take you there… hehehe…”

or "heeheehee"

She said that whilewas smiling wildly, chuckling at me. She was smiling wildly, chuckling at me.

She said that while smiling wildlywas smiling wildly as she said that, chuckling at me. She was smiling wildly as she said that, chuckling at me.

I was afraid when I heardHearing her voice and saweeing her expression so, I was so afraid that I suddenly yelled at her, and then woke up. Hearing her voice and seeing her expression, I was so afraid that I suddenly yelled at her, and then woke up.

More natural

I was afraid when I heard her voice and saw her expression, so I suddenly yelled at her and woke up. I was afraid when I heard her voice and saw her expression, so I suddenly yelled at her and woke up.

I had overslept in thise campus library until six in the evening. I had overslept in the campus library until six in the evening.

I overhad fallen asleept in thise campus library until six in the evening. I had fallen asleep in the campus library until six in the evening.

"Oversleeping" generally implies the morning

It happenedAll because I was so caught up in daydreaming that I ended up feeling tired and overslept. All because I was so caught up in daydreaming that I ended up feeling tired and overslept.

"It happened because" sounds oddly stiff

It happened because I wasd been so caught up in daydreaming that I ended up feeling tired and overslfalling alseept. I had been so caught up in daydreaming that I ended up feeling tired and falling alseep.

I needed to be more focused so that I wouldn't get lost in a daydreaming again. I needed to be more focused so that I wouldn't get lost in a daydream again.

“God, why did I dream of Alana with her pale face andface super pale, and that scary expression? “God, why did I dream of Alana with her face super pale, and that scary expression?

You said Alana is pale normally, so saying "Alana with her pale face" sounds odd, like "Alana with her blue eyes." In the dream I think she was even more pale, which is what makes it notable to mention here. Without "that" it sounds like you're saying Alana always has a scary expression. This clarifies that the scary expression was unique to the dream

It wasHow crazy!” How crazy!”

Sorry, it's hard to explain why "It was crazy!" sounds weird here ):

I was so nervous and worried because I was alone there in the library. I was so nervous and worried because I was alone there in the library.

You use "there" because presumably the narrator is not currently in the library, so from their perspective (looking at the past from the future) it would be "there" not "here"

I was so nervous and worried because I was alone here in the library. I was so nervous and worried alone here in the library.

I looked around at the bookshelf, tves. The atmosphere was really dark and empty. I looked around at the bookshelves. The atmosphere was really dark and empty.

I looked around at the bookshelf, t. The atmosphere was really dark and empty. I looked around at the bookshelf. The atmosphere was really dark and empty.

Everyone must bhave already been gone, because of this situation, Iand that observation made me hurriedly packed my stuff and goet ready to leave. Everyone must have already been gone, and that observation made me hurriedly pack my stuff and get ready to leave.

It's unclear what "this situation" refers to and it's unclear if the situation is the reason for everyone being gone or if it's the reason for hurriedly packing your stuff. I assumed the latter for my correction.

Everyone must bhave already been gone, because of this situation,so I hurriedly packed my stuff and got ready to leave. Everyone must have already been gone, so I hurriedly packed my stuff and got ready to leave.

It madgave me feel goosebumps. It gave me goosebumps.

It madgave me feel goosebumps. It gave me goosebumps.

Her face looked very familiar to me, but maybe itI was just my imaginationaking things up. Her face looked very familiar to me, but maybe I was just making things up.

I think "it was just my imagination" and "I was just imagining things" are more for situations where you think you sense something (hearing a sound, seeing something in the corner of your eye) but you can't confirm if it actually happened. It has the feeling of hallucinating an occurrence. I wouldn't use it for recognizing a face.

I had better not think of strange thoughtsanything strange right now. I had better not think anything strange right now.

I had better not think of strange thoughts right now. I had better not think strange thoughts right now.

I ought to bjudge people more rational about judging someonely. I ought to judge people more rationally.

But I didn't mean to judge her in a bad way. But I didn't mean to judge her in a bad way.

I would end the previous sentence with a comma and continue with this one, rather than separating them.

It was so relaxing that I could sit andBeing able to spend my time alone in my favorite place, in this secluded comfortable corner of the library without hearing about suchthe annoying gossip that was always spread by my classmates - it was so relaxing. Being able to spend my time alone in my favorite place, in this secluded comfortable corner of the library without hearing about the annoying gossip that was always spread by my classmates - it was so relaxing.

The original word order made the meaning a little ambiguous - it could be construed as saying that it being relaxing was the reason that you were able to sit in your favourite place

It was so relaxing that I could sit and spend my time alone in my favorite place, in this secluded comfortable corner of the library without hearing about suchthe annoying gossip that was always spread by my classmates. It was so relaxing that I could sit and spend my time alone in my favorite place, in this secluded comfortable corner of the library without hearing the annoying gossip that was always spread by my classmates.

You could also say "... that my classmates always spread" for brevity's sake, but either way works.

But I must be serious about my responsibilities, instead of staying in my comfort zone. But I must be serious about my responsibilities, instead of staying in my comfort zone.

This sentence kind of comes out of nowhere, I think "but" is a good conjunction (technically grammatically incorrect to start a sentence with "but", but all that goes out the window in creative literature) to tie it in because it contrasts wanting to be in the library (comfort zone)

While reading a book, I my mind wandered, and I began to wondered if I could be someone else. While reading a book my mind wandered, and I began to wonder if I could be someone else.

It feels a little weird to use "while" because the character is likely not actually reading if they are thinking deeply about something

I hoped I could talk with that new transfer student, Alana, because she was really outgoing and not afraid to take a chance to meeting new people. I hoped I could talk with that new transfer student, Alana, because she was really outgoing and not afraid to take a chance to meet new people.

I hoped I could talk with thate new transfer student, Alana, because she was really outgoing and not afraid to take a chance meeting new people. I hoped I could talk with the new transfer student, Alana, because she was really outgoing and not afraid to take a chance meeting new people.

Alana reminded me of my best friend I used to have named LunaLuna, who used to be my best friend. Alana reminded me of Luna, who used to be my best friend.

Original isn't wrong, and you often hear stuff like that in speech, but in writing it comes off a little clunky.

Alana reminded me of my old best friend I used to have named, Luna. Alana reminded me of my old best friend, Luna.

My best friend always encouraged me in the past, told me that I could do anything I wanted to by myself. My best friend always encouraged me in the past, told me that I could do anything I wanted to by myself.

And righBut now, I washad become used to being alone after she'd left. But now, I had become used to being alone after she'd left.

She really disappeared without a single text after she movedmoving somewhere else with her father somewhere else six years ago. She really disappeared without a single text after moving somewhere else with her father six years ago.

She really disappeared without a single text after she moved somewhere else with her father somewhere else six years ago. She really disappeared without a single text after she moved somewhere else with her father six years ago.

I would've liked to forget about her but I couldn't. I would've liked to forget about her but I couldn't.

I was lost in thought, remembercalling the memories aboutof my best friend, but all of the sudden, Alana, suddenly stood beside me. I was lost in thought, recalling the memories of my best friend, but all of the sudden, Alana stood beside me.

"sudden" and "suddenly" together is redundant

I was lost in thought, remembering the memories about my best friend, but all of thea sudden, Alana, suddenly stood beside me. I was lost in thought, remembering the memories about my best friend, but all of a sudden, Alana suddenly stood beside me.

Her face looked paler than usual, s. She stared at me with a blank expression that made my heart race. Her face looked paler than usual. She stared at me with a blank expression that made my heart race.

“What’s wrong with her?” I askedthought to myself. “What’s wrong with her?” I thought to myself.

"asking yourself" sounds a little weird unless you're think something self-reflective. Like: "Why did I do that? How could I have done something so horrible?" I asked myself.

The more I sawlooked at her pale face, the more I felt afraid of her. The more I looked at her pale face, the more I felt afraid of her.

I was not used to staybeing in the library untilat this hour. I was not used to being in the library at this hour.

While I was putting my things into my bag, I accidentally knocked my pencil case off the table, and it fell to the floor under the library table. While I was putting my things into my bag, I accidentally knocked my pencil case off the table, and it fell to the floor under the table.

Using "knock" without a preposition sounds weird Specifying that it's a library table is odd

While I was holding my phone to turn onUsing the flashlight on my phone, I knelt down and was about to pick up my pencil case. Using the flashlight on my phone, I knelt down and was about to pick up my pencil case.

But then, I felt a suddenly jolted when I touched something strange under the table. But then, I suddenly jolted when I touched something strange under the table.

"felt a sudden jolt" feels like the jolt is coming from an external source, but I think you mean the narrator jolted in surprise

I stumbled backward because I was, terrified. I stumbled backward, terrified.

I pointed my phone flashlight again under the table again to see it clearly, thinking that I might be hallucinating. I pointed my phone flashlight under the table again to see it clearly, thinking that I might be hallucinating.

At that moment, the same hoarse creepy voice I'd heard in my dream came out of nowhere, followed by a soft touch on my shoulder. At that moment, the same hoarse creepy voice I'd heard in my dream came out of nowhere, followed by a soft touch on my shoulder.

“Hihihiehehe… I told you not to daydream!” “Hehehe… I told you not to daydream!”

“Hihihiehehe… I told you not to daydream!” “Hehehe… I told you not to daydream!”

I looked at the source of that creepy voice and I almost fainted when I realized it was Alana. I looked at the source of that creepy voice and almost fainted when I realized it was Alana.

I looked at the source of thate creepy voice, and I almost fainted when I realized it was Alana. I looked at the source of the creepy voice, and I almost fainted when I realized it was Alana.

She smiled at me in a disturbing way while she was pointing at me. She smiled at me in a disturbing way while pointing at me.

She started laughing in a creepy way,creepily, and then I let out a loud scream and said, “Go away. She started laughing creepily, and then I let out a loud scream and said, “Go away.

Just to avoid the repetition of "in a ___ way"

But she was just mumbling something unusualstrange while walking towards me, smiling wildly. But she was just mumbling something strange while walking towards me, smiling wildly.

"unusual" = uncommon. It doesn't have a negative association either

My tTears were streaming down my face in this terrible situation. Tears were streaming down my face.

I don't know if this is a language critique or a writing critique xD But I think "in this terrible situation" breaks the reader's immersion in the scene; it feels like we suddenly went from inside the character's head in the moment to a third person perspective objectively looking back at a memory

“Hihihiehehe… I… told you… not to daydream…” “Hehehe… I… told you… not to daydream…”

“Hihihiehehe… I… told you… not to daydream…” “Hehehe… I… told you… not to daydream…”