Hi ansarkhan1,
You've posted a number of different times recently - describing different concerns and issues that you're facing. I'm going to try to answer all of those concerns in this one post:
To answer your immediate question: if you find that you are making some careless errors during the first couple of questions of your Exam, then the root 'cause' is likely your 'organization' (how you take notes, the Tactics that you use, etc.); in addition, doing work "in your head" is the WORST way to approach a GMAT question, so you should NEVER work that way. You might find it helpful to do a few 'warm up' practice questions BEFORE you begin your CATs - in that way, you can get yourself mentally prepared for the work that you'll have to do over the next several hours.
Beyond that, raising a 520 to the point that you can consistently score 670+ will likely require at least another 3 months of consistent, guided study - and you'll have to make significant improvements to how you handle BOTH the Quant and Verbal sections. Thankfully, the GMAT is a consistent, predictable Exam, so you CAN train to score at a higher level. Trying to make all of those improvements in just 1 month is likely be too difficult to be considered realistic, so you might want to consider pushing back your Test Date. There's no harm in taking the GMAT in one month, but you can save some time, money and aggravation by rescheduling.
Since you've been studying for 6 months already, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) 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) When are you planning to apply to Business School?
5) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich