Hi jgnorero,
First off, a 680 is a great score (it's just a bit below the 90th percentile overall) - and it is likely strong enough to get you into Business School. As such, you might not need to retest.
The GMAT is remarkably good at giving each Test Taker the score that he/she has EARNED. This time around, you did enough to earn a Q46 - this is still a strong performance, but you made enough little mistakes (likely on DS questions, but you probably missed a couple of 'gettable' PS questions too) to miss out on those remaining points.
Since your original score was a year ago, what type of studying did you do for this latest attempt:
1) How long did you study?
2) What resources did yo use?
3) How much of your time was spent on Verbal and how much was spent on Quant?
GMAT assassins aren't born, they're made,
Rich