Hi mariebelle,
Yes - you can retake the GMAT in 16 days (whether you cancel this recent Official Score or not). That having been said, retaking the GMAT so soon might not be the best idea - especially if you have not determined WHY you scored lower than you wanted to (and worked to 'fix' whatever issues are currently keeping you from scoring higher). Thus, 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)?
4) How did you score on the Official GMAT (including the Quant and Verbal Scaled Scores)?
Goals:
5) What is your goal score?
6) When are you planning to apply to Business School?
7) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich