Hi GMATDemiGod,
First off, a 680/Q46 is a strong score (it's well above the 80th percentile overall), so it could be enough to get you into one of the Schools that you listed. You named some really competitive Schools though, so you have to make sure that you have a strong OVERALL application AND that you properly 'market yourself' to each Admissions Committee.
GMAC has publicly stated that the Official Score that you earn on Test Day is within +/- 30 points of actual ability. This means that your Official Score is almost the same overall performance (+ or - a few correct answers on certain questions). By extension, you could have easily scored 710+ on Test Day, but you made a few too many little mistakes.
You still have plenty of time to continue studying, if you choose to retest though.
1) How long did you study?
2) What resources have you used so far?
GMAT assassins aren't born, they're made,
Rich