Hi prabsahi,
You mentioned that you were just getting back into your studies. Can you go into a bit more detail about how you studied before? What type of study routine were you following and what specific areas did you work on?
There's no 'harm' in taking the Official GMAT on August 31st - although that's a relatively expensive way to take a 'practice test.' Many Test Takers spend 3 months (or more) of consistent study time before they hit their 'peak' scores - and since you're not planning to apply until Round 2, you have plenty of time to study and improve - which is good. If you haven't taken any practice CATs/mocks yet (not even during your prior studies), then there's really no way to know what study materials you might 'need' right now. That having been said, with a Score Goal of 740+, you're after a Score that approximately 97% of Test Takers never achieve (regardless of how they study or the number of times that they take the Official Exam), so you would likely find it beneficial to invest in a GMAT Course of some type (either Guided Self-Study or instructor-led.
To be efficient with your study time going forward, I highly recommend that you take a FULL-LENGTH practice CAT sometime soon; you can take 2 for free at
www.mba.com (and they come with some additional practice materials). That score will give us a good sense of your natural strengths and weaknesses and will help provide a basis for comparison as you continue to study. A FULL CAT takes about 3.5 hours to complete, so make sure that you've set aside enough time to take it in one sitting. Once you have those scores, you should report back here and we can come up with a study plan.
GMAT assassins aren't born, they're made,
Rich