Hi sunny216,
There are a couple of issues to discuss:
1) You mentioned wanting to apply to a Top 10 School - and you seem to understand that having a strong GMAT score will be necessary. Highly-competitive Schools tend to view the Quant Scaled Score as a measure of an applicant's ability to handle the 'academic side' of the Program. As such, you do not want to apply with a 'weak' Quant Scaled Score (since that might be viewed as a 'red flag'). While you could certainly score 700+ with a stronger Verbal and a weaker Quant, that 'combination' might actually work against you if the rest of your application isn't strong enough to compensate for a lower Quant Score.
2) Your Test Date is in about 10 days. If your score goal is 700+, then it's not likely that 10 days will be enough to raise a 620 to that level.
3) Many Test Takers spend 3 months (or more) of consistent study time before they hit their 'peak' scores. From what you've described, you're close to about 2 months of study.
Considering the above points, you might want to consider pushing back your Test Date - so that you can continue to study and hone your skills (and improve your Quant skills as much as possible).
1) What is your goal score?
2) When are you planning to apply to Business School?
3) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich