Hi juniorsbc,
If you cancel your score when you take the Official GMAT, no Business School will ever know that you even took that Test.
Since you referred to having some trouble in the Quant section, I assume that you've put in some study time already. Before I can offer you the specific advice that you're probably looking for regarding your overall studies, 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 materials have you used?
3) How have you scored on each of your CATs (including the Quant and Verbal Scaled Scores)?
Goals:
4) What is your goal score?
5) When are you planning to retake the GMAT?
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