What is your goal score? That will change my advice - there are things you can do to lift your score in 3 weeks, but there are limits. It's unlikely, for example, that you will lift to a 700 in 3 weeks. Even 650 is probably a stretch.
The first step is to analyze your data to figure out where you need to get better.
First, read these two articles:
https://www.manhattangmat.com/blog/2013 ... lly-tests/http://www.manhattangmat.com/blog/2013/ ... -the-gmat/Think about how what you've been doing does and doesn't match up with that and how you may need to change your approach accordingly.
Then, use the below to analyze your most recent MGMAT CATs (this should take you a minimum of 1 hour):
http://tinyurl.com/analyzeyourcatsBased on all of that, figure out your strengths and weaknesses as well as any ideas you have for what you think you should do. Then come back here and tell us; we'll tell you whether we agree and advise you further. (Note: do share an analysis with us, not just the raw data. Part of getting better is developing your ability to analyze your results - figure out what they mean and what you think you should do about them!)