As a general rule, you should expect to score on the real test roughly (+/- 50 points) what you're scoring on practice tests in the last 7 to 14 days before the real test.
This assumes that you have taken the practice tests under 100% official conditions,
including essays. If you took the tests under non-official conditions, including skipping the essays, then your practice scores might be inflated and you are more likely to get a lower score on the real test.
That means you have some bad news - if you still want to go for that 650, then your best bet is to postpone your test. Because you're still more than 7 days away from the test, you can reschedule it by paying a fee of $50. If you wait until you're within 7 days of the test, they will charge you the entire $250 again.
I know this isn't what you want to hear, but it's better to know what you're up against so that you can make good decisions now.
Next, if you want advice on how to improve, then we need data from you about your strengths and weaknesses. Do the analysis described in the below article on your most recent MGMAT test. If you deviated from official test conditions in ANY way, include that information in your post.
http://www.manhattangmat.com/articles/e ... -part1.cfmNote: make sure to post your analysis - what you think the data means for you - and not just the data itself. One skill you need is the ability to assess your strengths and weaknesses very specifically and figure out what steps to take in order to improve. We can help you do that, but you do need to learn to do it, too. :)