I'm sorry you're having such a difficult time with this test.
Start here:
http://www.beatthegmat.com/a/2009/10/26/my-score-dropped-figuring-out-what-went-wrongWe first need to figure out why you're scoring 100 points below your practice test scores when you take the real thing. Do the analysis described in the above article and come back here to tell us what you discovered.
Second, if you've taking an MGMAT practice test in the past month, read this article and do the analysis described:
http://www.beatthegmat.com/a/2009/09/23/evaluating-your-practice-testsThis will help us to get more detailed info on your strengths and weaknesses. Again, come back and tell us what you discovered from this analysis.
Note: you'll be typing up several paragraphs (at least) of information. You may want to save all of this in a Word file as you do the analysis, and then cut and paste to create a post here.
Once we have all of this data, we can use it to figure out what to do from here.