Hi ashutosh1617,
To start, a 690/Q50 is a fantastic score (it's just shy of the 90th percentile overall), so it could very well be enough to get you into your first-choice Business School. As such, a retest might not be necessary.
1) What Schools are you planning to apply to?
2) When are you planning to apply?
GMAC has publicly stated that a Test Taker's Official Score is within +/- 30 points of actual ability. Assuming a similar 'swing' in how your CATs scores, and that you took your CATs in a realistic manner, your 690 is 'in range' of 720 (albeit at the low end of the range). At your scoring level, the GMAT becomes really 'sensitive' to little mistakes - you made a few too many on Test Day and your score dropped because of it.
1) How many Total CATs did you end up taking during your studies?
GMAT assassins aren't born, they're made,
Rich