In high school, I took four APs. (US History, Spanish, English lit, and, yes, calculus) About the calculus one, I felt the multiple choice was bad, but not that bad. The free response was extremely difficult though. Just don't lose your cool. You won't be able to answer every question. Just take it easy and play around with the problems. (You'd be amazed how well that works sometimes) Most of all, DON'T RUSH!!!! You don't need stupid mistakes on your test. I thought I did awful, but I ended up with a 4, so don't sweat the difficulty.
About the US History, you get choices on the essays, so I'm sure you'll get a question you like. As I remember (This exam was two years ago, so I might be mistaken) the worst part of the History exam was that my hand was falling asleep while writing the essays. (Just make sure you know the difference between World War ONE and World War TWO.
)But, if your school is like mine, they'll give you the rest of the day off, so go out to a nice lunch, enjoy the afternoon, and remember that the exams in college are nowhere near as bad as the APs. Good luck to all of you in high school that have to take those tests from hell. Just remember that nobody knows all of the answers.