I think that both the Kaplan Step 1 Simulation CD and Kaplan Step 1 Q-bank are significantly more difficult than the actual exam. In my opinion, the 150 question NBME Released Items CD is much more representative of the real exam. However, that's not to say that your purported 50% on the Kaplan CD isn't something to worry about... I'd estimate that that's just barely passing if you were to take Step 1 tomorrow. My advice... don't get hung up on your scores from Kaplan mcqs, but do use these 3 weeks wisely and try to improve your %es to at least 60-65%. Good luck.