GMATPrep is the real deal, your score might be +/-30 of gmatprep score

The GMATPrep score is the one that you need to concentrate on. Unofficial practice tests are not to be used for predicting your score on test day.

There are several things that you need to consider when evaluating your GMATPrep scores. How many questions did you miss on the Quant? How many of these were easily avoidable errors like answering the incorrect question and calculation errors? Are there particular areas in the quant that you simply do not currently understand? In other words, are there changes that you can make that will produce quick results, either by shoring up your knowledge in one or two areas and/or by being methodical and avoiding those "silly errors."

On the Verbal side look back through and see which of the three areas was your weakness - or perhaps there are problems in all three. Did you make some easily correctable mistakes there?

You need to decide now if you can make some serious improvement in the next few days, or if you should postpone the test. You need to change the date 7 days in advance in order to only be charged $50. That would mean moving the date tonight. Another possibility is taking the exam in a week and realizing that you will likely be retaking it is 31 days - the minimum number of days between attempts.

Good luck!