A Chinese student in Grade 12 is faced with university entrance exams

Today is so horrible because l feel stressed!Every student in Grade 12 may feel like that,but l have never thought l could be a stressed student,especially when l didnt get high grade in exams. l wasnt didn't feel bad about it cuz (because) it wasn't a big deal.
ln China,whether you can be remarkable,it all depends on the university you are or were in.l dont think so though.
Because l am in Grade 12,now,no matter what else l want to do,my teachers and parents would warn me:"Oh,come on,you are going to be a college student!"That means that l shouldnt have something spending waste my spare time,and they think l am supposed to do my homework instead. Who knows what the hell they are thinking about?
l ever once heard of a saying:Ignorance is bliss.What if l ignore their warning,my future will be ruined,but every time (2 words, not "everytime") when l hear my mom says:''You must go to a top university."Gosh,l have had enough of this.
l want a good university,but dont know why. l dont feel the importance of a university,it is just a place for me to study after l finish my high school.Our society is cryel cruel,so l have no choice but to work hard and enter a good university.
Chinese education is a little hard on students. If god gave me a chance to be reborn,l would be Chinese again,but l wouldnt be a Chinese student!

Very good! I understood everything you wrote.

Please be careful about using " , " too much:  If you do it, like this, you can make a sentence, that is really long, but that is not correct, because if you say it out loud, it will sound strange, don't you agree?

Try to use "." and start a new sentence.

Apart from that, great work! A+

I hope your studies become more easy in College or University, or that you manage to have fun while you study. :)

A Chinese student in Grade 12 is faced with (facing) university entrance exams

Today is so (absolutely) horrible, because l feel stressed!  Every student in Grade 12 may feel like that this (the same way), but l have never thought that l could be a stressed student; especially even when l didn't gethigh grades in my exams, l wasnt didn't feel bad (about it) cuz because it want wasn't a big deal (to me.)

ln China, whether you (one) can be remarkable successful or not, it all depends on the university you are (one is) or were (was) in.  l dont think so, though. (I, however, disagree.)

An alternative: In China, it is widely believed that one's future success depends on the university that one went to.  [I, however, disagree / I beg to differ.]  The underlined part is needed to clarify that the idea of success depending on one's university is an opinion.  This ensures that the later part, where you disagree with the opinion, make ssense.

Because l am now in Grade 12 now, no matter what else l want to do, my teachers and (my) parents would warn me: "Oh, come on! You are going to be a college student!" That This meansthat l shouldn't (am not allowed to / can't) have something (anything) planned during spending my spare time;,and they think (that) l am supposed to should do my homework instead, but who knows what the hell they are thinking (about)?
l ever have heard of a saying (There is a saying that I've heard of): Ignorance is bliss.  What if l ignored their warnings?  My future will would be ruined, but everytime every time when l hear my mom says say, ''You must go to a top university," I think, "Gosh, l have had enough of this."
l want to go to a good university, but I don't know why; l don't feel understand the importance of a university (why university is so important).  It is just a place for me to study at after l finish my high school.  However, Our society is cryel cruel, so l have no choice but to work hard and enter a good university.
The Chinese Education System is a little hard on the students; if God gave me a the chance to be reborn, l would choose to be Chinese again, but l wouldn't choose to be a Chinese student!

This is really well written!  I can sort of empathise with you, as it was not so long ago that I was facing my final exams at Sixth Form to get into university!  It is important to get a balance between working and relaxing; too much of either isn't good!  I hope that your exams go well for you!  :)