Hi Sabybhowmick,
First off, a 650 is a strong score (it's right around the 80th percentile overall), so it could be enough to get you into your first-choice School. As such, a retest might not be necessary. You're ultimately asking Admissions questions though, so you would likely find it beneficial to speak with an Admissions Expert about your overall profile. There's a Forum full of them here:
ask-admission-consultants-124/Since the process of applying to (and attending Business School) involves a significant investment of time, money and energy on your part, you really should do some research to determine which Schools are a good match for YOUR career goals (as opposed to just applying to School in which you 'would probably get in').
If you do want to retest, then it would help if you provided a bit more information about how you studied:
1) How long have you studied?
2) What materials have you used?
3) How have you scored on each of your practice CATs (including the Quant and Verbal Scaled Scores)?
4) What were your Quant and Verbal Scaled Scores on the Official GMAT?
GMAT assassins aren't born, they're made,
Rich