Hi miridom,
Many GMATers feel some type of frustration during their studies, so you're not alone. 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) Is the 510 you referred to from a practice CAT/mock or from the Official GMAT?
2) How long have you studied in total? Over the last 3 months, how many hours did you typically study each week?
3) What study materials have you used so far? What “brands” of CATs/mocks have you used?
4) On what dates (or approximate dates) did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
5) When are you planning to apply to Business School and what Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich