If it helps any, remember that you are the best. Only one out of ten applicants actually made it in, so there are nine people sitting at home wishing they were you. The Academy's admissions experts believe you can succeed. If they didn't, they wouldn't have given you the opportunity. Think hard now about why you want to do this so that you can remember later when things get tough. And if you do think about quitting, *please* sit down and really think about it before making a decision. If you quit, you will have to live with that decision from now on. And believe me, regrets and "what ifs" don't go away.
Lean on your friends and classmates. Remember too that there are supportive folks out here in lj-land. Use us.