I'm a DPM taking the MCAT to become a DO or an MD. I haven't had these classes (physics, bio, chem) in over 10 years! Believe me, I'm wetting my pants, too!!
What's giving me the most trouble is the friggin' physics!!!!!!!!!!!!!!!!!!!!!!!!!!! Newtonian Mechanics just simply sucks copious bunny farts! And, I took O-chem in a 10 week summer course, which means that I didn't understand a thing! The only test I've taken so far is the on-line MCAT where I got a 7 on physical sciences. Not horrible.
I think what the previous poster said is the right thing. It's all about confidence! You know more than you think you do. Just go in there relaxed. You won't believe what'll come to your mind!