Hi
I am pretty sure you need to contact AGUSM directly about doing the Kaplan review through them. Maybe you get a tuition discount being a student. I also know that Kaplan offers numerous courses to prep for USMLE just check out their website. Either way I recommend you set yourself up for success by taking a few practice tests and see where you are. USMLE step 1 is a monster of a test and designed to determine everything you know and don't know about medicine. Some people try to put-off studying until too late. I did pretty well and I started really studying about 3 months before. I was just an average student during the first two years but during those 3 months I really put everything together. I never took Kaplan because I felt comfortable that I could organize my own study plan.
Don't be afraid. Be smart. It's just like any other test, multiple choice, the answer is there somewhere. It's just REALLY BIG.
Good luck,