You can absolutely say "I am feeling a little bit nervous"

Not correct to say "I don't know what my English level is at", must be instead "I don't know where my English level is at", but this sounds bad, so avoid it

Firstly

Names must have capitals, even internet names. "My internet name is Ziye and I'm 24 years old. I'm currently doing my masters at university". You study "at" a uni not "in" a uni.

This wasn't correctly corrected! If you are not fluent please don't correct it!

Using "first" was correct in this sentence, and there is even a preference for it in written English in certain cases: https://www.merriam-webster.com/words-at-play/first-or-firstly#:~:text=Even%20though%20they%20are%20both,the%20best%20bet%20for%20most

https://dictionary.cambridge.org/us/grammar/british-grammar/first-firstly-or-at-first

Degrees are not something you get at school. This is incorrect. You get them at universities only.

We often say "school" for shorthand in the US even if we mean college/university or grad school, so while you're technically correct that degrees are usually only given from higher ed institutions, using "at school" isn't necessarily incorrect, and people would know that ziye isn't referring to elementary or secondary school when saying "at school".

Using "first" was correct in this sentence, and there is even a preference for it in written English in certain cases: https://www.merriam-webster.com/words-at-play/first-or-firstly#:~:text=Even%20though%20they%20are%20both,the%20best%20bet%20for%20most

https://dictionary.cambridge.org/us/grammar/british-grammar/first-firstly-or-at-first

Good point, but I don't think this is widely understood outside the us

Well, not to be too rude or anything, but since I am an American, I correct using the standard I speak/write. I assume that's the same for speakers of other varieties of English (British English, for example). In general, perhaps you shouldn't correct other native speakers' corrections unless there's actually a mistake (saying "a eyebrow" instead of "an eyebrow") and not just a dialectal difference, especially since you corrected things in both my and Curisosity345's corrections that were actually correct/didn't need any correcting.

Sorry, I corrected the mistakes I saw, in order to help the original writer. American english is correct but not standard everywhere, so shouldn't be seen as so

No worries! I understand you were just trying to be helpful.

And yes, I understand that American English is not the only English that's correct and shouldn't be seen as so, but as I said, since I'm a native speaker of American English and not of another variety of English, I only correct things using the standards of American English. I do know there are spelling and syntaxial differences among all varieties of English, so, for example, if someone wrote "colour" instead of "color", I wouldn't correct it. On the other hand, we have no way of knowing which standard of English the writer is learning, unless they state so in their profile or entries, so sometimes it can be hard to differentiate if someone is making a mistake or using a feature that's common in a different standard of English.