Hi Abhishek,
First off, a 680 is a strong score (it's right around the 85th percentile overall), so it could certainly be enough to get you into Business 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/GMAT assassins aren't born, they're made,
Rich