Hi nivedita88,
Many Test Takers spend 3 months (or more) of consistent study time before they hit their 'peak' scores, so if you've really been studying for just one month, then you just have not put in enough time and effort to have scored higher yet. By extension, it stands to reason that you would likely continue to improve as you continue to study.
All of that having been said, raising a 640 to a 740+ will likely take at least another 2 months of consistent, guided study - and you'll have to make significant improvements to how you handle BOTH the Quant and Verbal sections. Based on what you have described, you had never taken a FULL-LENGTH practice CAT in a realistic fashion before you took the Official GMAT. As such, your Official GMAT is your 'baseline' score; and all things considered, it's really strong for an initial score.
1) When you say that you will not apply to Business School until you score at least a 700, are you comfortable with the idea that you might not apply until a year from now (or would you consider applying for Round 2 now if you scored 680 or 690?)?
2) Going forward, how many hours do you think you can consistently study each week?
GMAT assassins aren't born, they're made,
Rich