my school also offers Exam master to us free of charge.
I used it in the last week (after having completed Kaplan Qbank, and done most of USMLEWorld) to go over my weak subjects (Pharm, immunology, microbiology). In retrospect, this was an excellent decision. The material that was tested was completely different from the pharm/immunology/micro that was tested in either Kaplan or UW. Thus, I learned a lot of new info (some of which was tested on my Step 1 exam).
So my advice is: do as many questions as possible before your test, since it is the fastest and most reliable way of learning new material and consolidating basic information. Exam master is a resource which nicely augments Kaplan and USMLEWorld (especially if it is free)