Hi Wataru,
It's certainly unfortunate that you might not be able to retake the GMAT until October - but you could potentially improve a great deal in the next 2 months, so you should be thinking in terms of how you can take advantage of that time to hone the skills needed to earn that higher Score.
I suggest that you start a new post/thread and provide a bit more information about how you've been studying and your goals (that way, the discussion can stay focused on YOUR situation). For example:
1) How long have you studied? How many hours do you typically study each week?
2) What study materials have you used so far?
3) On what dates did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
4) What is your overall goal score?
5) When are you planning to apply to Business School and what Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich