Your friend is a natural at standardized tests. It is VERY unusual to get such a high score at all, let alone after studying for 3 weeks. Most people study for 2 to 4 months (and not everyone hits their target score, even after all that study).
So, I have bad news for you. You're currently scoring around 600 on practice tests and you want to get a 700. The vast, vast majority of students would not be able to make that kind of jump in 3 weeks. My best advice to you is that you are going to have to make a choice: take the test in 3 weeks, but with a more realistic goal score, or postpone the test to go for the higher goal score.
I know that's not what you want to hear, but it's better to know right now than to continue to plan for an unrealistic outcome.
You're going to have to decide what to do on the above. We can give you advice on how to improve, but that advice will depend upon whether you stick to the three weeks with a lower goal score or whether you give yourself more time but want to go for the higher goal score. Let us know.
Also, do this analysis on your most recent MGMAT practice test:
http://www.manhattangmat.com/articles/e ... -part1.cfmIf you want our help, please post your analysis here. Note: our practice tests are not significantly easier or harder than the real test. Some people say they're easier and some say they're harder, which generally means they're about in the middle. :)
Also note: if you did not take your practice tests under official test conditions, your score could be less valid or even inflated. If you skipped the essays, for example, or took longer breaks than allowed, or used the pause button - any of those things could give you a scoring advantage that you would never have on the real test. If you have not already gotten into the habit of taking practice tests under 100% official conditions, please do so going forward.