Hi ashutoshsh,
From what you've described, it sounds like you've been trying to self-teach the material, which is why you're currently 'stuck' at this level. To score at a much higher level, you'll need consistent guidance and you'll need to focus on learning/practicing the necessary Tactics for both the Quant and Verbal sections. Since you have NOT been taking the FULL CAT each time, you've taken a shorter Exam that requires less work from you (and if you do the Quant sections untimed, then that too is unrealistic), so your scores are likely not completely accurate. This is all meant to say that pushing back your Test Date so that you can study properly is a good idea. Based on the work that you've done so far, you will probably need at least another 2 months of consistent, guided study to hit your score goal.
1) What Schools are you planning to apply to?
2) How many hours do you study during a typical week?
GMAT assassins aren't born, they're made,
Rich