If it’s not too late, finish the class. I couldn’t tell from your post if you’d a) already dropped or b) simply already emailed Rice. I looked at Total Registration data and 43.9% of those who took the CS AP last year got a 4 or a 5. Buy a prep book or two and spend a little time studying on your own. If you have already dropped, how long ago? Can you see if you can get back in? I’m assuming you’ve already paid the fee to take the exam, too…