First of all, RELAX! Your Kaplan class hasn't even started yet. You are also not supposed to start answering the Question Trainers yet, only the pretest. I passed with Kaplan and took the class. Try to follow the schedule they give you (they will discuss it in your first class). I read the entire Kaplan book just to refresh my memory. Obviously, not all at once. When you are reading, if there are areas you feel comfortable with, skip over them. And if something seems fuzzy to you, then brush up on that area. Also, pay attention to the Decision Tree. I felt that it really helped me learn how to answer questions. After my Kaplan class, I did about 60 questions a day. If you get a question wrong, make sure you understand WHY you got them wrong. Also, understanding concepts is way more important than memorizing facts.
So, take a nice big deep breath and relax! You are only at the very beginning of your studying. You have time to be prepared and you WILL be prepared by the time you take your exam.