Hi amysong,
First off, a 670/Q48 is a strong score - and it could be enough to get you into your first-choice School. As such, a retest might not be necessary. In general, Business Schools do not care if applicants take the GMAT more than once, so having this Score on your record shouldn't be an issue. Assuming you were to raise this Score and hit your Goal Score, then you can actually use the two Scores to your advantage (your commitment to work harder and earn a higher Score is a character trait that you can use to 'market yourself' to the Admissions Committees).
As it stands, you're closer to a 730+ than you probably realize, but you will likely have to make some significant adjustments to how you handle BOTH the Quant and Verbal sections. Before we can discuss how you might best proceed, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How long have you studied?
2) What study materials have you used so far?
3) How have you scored on EACH of your CATs (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
4) When are you planning to apply to Business School?
5) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich