If your test is tomorrow, there is nothing that will help you more than a good night's sleep. If you aren't confident that you will ace the test (i.e. you have consistently done well on realistic practice exams), I would suggest rescheduling or withholding your score and studying for a solid 3 months before taking it. Take a class (Kaplan, Princeton Review, etc)...they really do work.
About me: I taught SAT,GRE,GMAT,LSAT for Kaplan for 6 years
Agree with @byoung2 about getting a good night's sleep. Try to keep yourself calm and focused for the exam. Give it your best shot, and don't feel afraid to complete the test even if you feel you haven't done well. IMO, that's a temptation that's hard to overcome no matter how well you're prepared. FYI: I took the test a few years ago (when the scoring system was based on 2400 points. Took the exam thrice & scored 1640, 1960, and 2340)