You're doing really well. Don't take more practice tests - you'll just tire yourself out and you're not going to learn much from taking a practice test in the last few days.
The standard deviation on our tests is about 50 points. The standard deviation on GMATPrep is likely around 30-40 points. (The SD on the real test is about 30 points.)
Also, it's fine to be nervous - everybody is. But do think about how you're going to keep yourself mostly calm so you can perform on the test. Here are some articles that may help:
http://www.manhattangmat.com/stress-tips.cfmhttp://www.manhattangmat.com/strategy-series-stress.cfmGood luck - keep up the good work and let us know how it goes!