Hi ozzykhan,
Based on the information that you've provided, and assuming that everything you have stated is accurate, then a School with an Average GMAT score of 600 would probably be unlikely to accept an applicant scoring in the 400-450 range.
There are some 'variables' in your situation though. Hopefully there's a way to define them so that we can come up with the best plan possible.
1) With a Test Date on April 9th (about 2 weeks from now), you're probably not going to score 600 (and you might not get close either). What is the LATEST that you can take your GMAT and still get your score in to the Admissions Office?
2) Has the Admissions Office given you any idea of the MINIMUM that you would need to score? This is a rather important piece of information as it would give you what could be an achievable goal in the short term. If there is any way for you to get this information, then that would be helpful.
3) What have your Quant and Verbal Scaled Scores been on your practice CATs?
GMAT assassins aren't born, they're made,
Rich