First, you can always change the date of your test if you haven't made the progress that you want to make by that date. (This is one of the biggest mistakes I see people make: they pick a specific test date months out, when it's impossible to tell exactly when you'll really be ready - and then they stick to that date no matter what. Give yourself the flexibility to take the test when you're actually ready!)
You'll need to do a detailed analysis to figure out why your score dropped. First, read these two articles:
https://www.manhattangmat.com/blog/inde ... lly-tests/http://www.manhattangmat.com/blog/index ... -the-gmat/Then, use the below to analyze your most recent MGMAT CAT (this should take you a minimum of 1 hour):
https://www.manhattangmat.com/blog/inde ... ts-part-1/Figure out your strengths and weaknesses as well as what you think you should do based on that analysis. 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!)
One common cause of a score drop is timing problems. Read these two articles:
http://www.manhattangmat.com/blog/index ... -to-do-it/http://www.manhattangmat.com/blog/index ... nt-part-1/And start doing what they say!
Our tests have a standard deviation of about 50 points (the real test has a standard deviation of about 30 points). They are directionally accurate, though not exact (none of these tests are, even the real thing!).