Hi sarkarpapia,
It's unclear whether SCs are the only subject that you need to improve on or not. In addition, you seem to understand why you're getting a lot of SCs wrong (some missing idiom knowledge and silly mistakes), so you should be able to work to 'fix' those particular issues (re: learn the idioms and practice enough so that you spot the necessary 'clues' to avoid the silly mistakes).
Before I can offer you any additional advice, 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?
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) What is your exact Official Test Date?
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