I took it in 2016 right after the class was introduced and it was very, very difficult. I was lucky to get a 5, but I would say that grinding out as many FRQs from past years as you can will help you. There are only so many concepts they can manage to test, and seeing them at least once should help you when you are actually taking the exam. Also, I would advise you to be familiar with the reference sheet even if you're given it, since you don't want to spend extra time looking over it wondering which equation might be good for a specific MCQ or FRQ. Review books might help, especially with practice MCQs (I recall always using Barron's for AP review).
Good luck. It's not an easy exam by any means, but I think you should be satisfied with your score as long as you know you made a good effort in studying and weren't slacking off during study time.