Hi madgame,
It's too late to cancel this Exam or reschedule it, so you should plan to take it as scheduled and do your best. If you're not happy with your result, then you can always cancel it - but you should note your score results (since they will be useful in planning out the next phase of your studies). In addition, you should pay careful attention to everything that's involved in your specific Test Day "event"; you'll be able to use that knowledge to better plan for your next attempt (assuming that one is needed).
Before I can offer you the specific advice that you’re looking for, 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) What Schools are you planning to apply to?
5) What are the exact application deadlines that you're facing?
GMAT assassins aren't born, they're made,
Rich