Hi amalganatra,
Many Test Takers spend 3 months (or more) of consistent study time before they hit their 'peak' scores, so it's likely that you just have not put in enough time and effort to have scored higher yet. Since your score goal is 650+, and you never scored higher than 530 on a practice CAT, there's some question as to why you did not push back your Exam. 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 have you used so far?
2) When are you planning to apply to Business School?
3) What Schools are you planning to apply to?
4) Going forward, how many hours do you think you can consistently study each week?
GMAT assassins aren't born, they're made,
Rich