Hi StijnO,
GMAC has publicly stated that the Official Score that you earn on Test Day is within +/- 30 points of actual ability. Assuming a similar 'swing' in how your CATs function, your 2 CAT score results show that you essentially performed the same each time (about 500 +/- a few points). You handle certain aspects of the GMAT consistently well, but you also make certain consistent mistakes. Raising a 500 to the point that you can consistently score 600+ will likely require at least another 2 months of consistent, guided study - and you'll have to make significant improvements to how you handle BOTH the Quant and Verbal sections. As such, you will likely need to push back your planned Test Date. Thankfully, the GMAT is a consistent, predictable Exam, so you CAN train to score at a higher level.
Before I can offer you the specific advice that you’re looking for, it would help if you could provide a bit more information on how you've been studying and your goals:
1) What study materials do you have access to besides the Official Guides?
2) When you say you "need" a 600, what does that mean exactly? Is a 600 the 'minimum Score' that you need to apply? Will that Score guarantee you entry into a particular Program?
3) Which Schools are you planning to apply to and what application deadlines are you facing?
4) Going forward, how many hours do you think you can consistently study each week?
GMAT assassins aren't born, they're made,
Rich