I'm a senior in high school and am taking IB courses (which are two year, college level courses). I take the IB exams in May. The exams cover all the information that I've learned since the beginning of my junior year of high school. May isn't for a while so I have other things at the forefront of my mind right now. I'm not too worried yet.

My advice to you is to take some deep breaths. If you've put in the study time and learned the material, that is all that you can do. Remind yourself that you've done what you can and leave it at that. There's no use worrying about the "what if's" if you have done the best you can to prepare for it. Breathe, eat well, get sleep the night before. And focus on the present when you take the test. Don't catastrophize.