The GMAT Club Tests
are tougher than the actual GMAT. Have you practiced Quant with other resources? The MGMAT test will provide a more accurate representation of the score you will see on test day, and the GMAT Prep is the best way to guage your progress.
From other posts, I gather Club Tests are a great way to improve your score. I have seen many talking about the 49-51Q they hit after working on the club tests. I scored 46Q on the GMAT Prep but am havingdifficulties similar to youers on the club tests. Hopefully the challenge will push us to the next level.