I am assuming that you scored a 41 on GMAT Prep. I scored a 44 on quant on GMAT Prep #2, which I took 2 weeks before the actual test. I scored a 48 on quant on the actual exam. While my results may be rare, the reason is probably due to the fact that I took my time on the first 10 questions on the real one but not the practice one. Make sure you get those correct, even if you spend up to 3 minutes on a couple of them...it has a HUGE effect. Also, do NOT leave any blank at the end of either section.
The only other advice I can offer is just to review the mistakes you have been making. However, I think once you reach a certain point in your quant skill level, the rest of your time should be spent on test strategies (pacing - getting first 10 right, but still finishing the test, guessing, etc).