Hi Prateek,
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 - and if you never scored higher than 640 on your CATs - then this Official Score isn't too much of a surprise. Your current 'ability level' is probably in the low-600s (+/- a few points).
Based on this score result, you have a great opportunity to pick up some serious points in the Verbal section. 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 your goals:
1) How have you scored on each of your CATs (including the Quant and Verbal Scaled Scores for each)?
2) What is your goal score?
3) When are you planning to apply to Business School?
GMAT assassins aren't born, they're made,
Rich