I think every law student has this same feeling after an exam. I should have done this, I didn't talk about that, I forget this, and it happens to everyone. I have gotten the highest grade in the class on a few occassions and had the same feeling of sh** I forget this issue or that issue and I did, but there are usually 16-20 issues and if you miss only one you are doing pretty well. As long as you wrote something coherent you should pass and generally law schools don't give out F's or D's if you really blew it you might get a C or C-.