GMATprep: How reliable is its scoring?

I downloaded the GMATprep software from mba.com a few months back and I finally felt that somehow I had to try it now or never, and got my score (690) and it was higher than I expected it to be, which is strange because I definitely had tougher questions on 800score (and a lower score).

I tried the score estimator but it did not have space for the GMATprep, so I would like to now how accurate you would say the GMATprep software would be.

Also, I purchased Cracking the GMAT by Princeton Review and it says (on the back cover) that I have access to four online practice tests, but the site seems to have only one practice test for me. Am I not looking in the right place?

Thanks for your time--I take the GMAT on Wednesday, and haaaaaa. I am afraid I have not been preparing for it as well as I should have been. :\