I felthought that I willould mess up.

"I thought" is more common to say in the US. This sentence is subjunctive case so that's why we use "would" instead of "will" here.

Everything today just made me feel exhausted.

Nevertheless, there was still something good which happeninged.

Receiving the TOEIC score is a singular event which happened in the past so this sentence is simple past tense.

That was I got aI received my TOEIC score, and it was higher than I had anticipated.

Congratulations!

This is more how'd we say it in the US.

Or more commonly used,

I received my TOEIC score and it was higher than I had expected.

Additionally, it also passed exchanging abroad thresholdIt also exceeded the threshold for international exchange programs for English.

Use either "additionally" or "also" but not both in the same phrase since they mean the same thing.

or, less commonly,

Additionally, it exceeded the threshold for international exchange programs for English.

It's a great encouragement to me feel so encouraged by it!

Everything today just made me feel exhausted.

ThaIt was that I got a TOEIC score, and it was higher than I anticipated.

Additionally, it also passed the exchanging abroad threshold for English.

It's a great encouragement to me!

Today, I spent the whole day preparing three subjects for tomorrow.

I feelt that I will mess up.

That was I got amy TOEIC score, and it was higher than I anticipated.

Additionally, itI also passed the exchanging abroad threshold for English.

It's a great encouragement tofor me!

Today I spent the whole day preparingstudying to be prepared for three subjects for tomorrow.

I felt that I willel like I am going to mess up.

Nevertheless, there was still something good that happeninged.

That was I got amy TOEIC score, and it was higher than I had anticipated.

It's a greatly encouragementing to me!