by 'powerprep' are you referring to the actual powerprep, or to the official GMATPrep exams from mba.com?

the powerprep software, which you can download here among other places, is now somewhat outdated; it was written by ETS, which doesn't have anything to do with the gmat anymore. the new software is GMATPrep (available from mba.com), which offers practice tests consisting of retired questions from fairly recent exams.

if you really mean GMATPrep when you say powerprep, then you should base your opinion much more on those tests than on the kaplan tests; not only did you study more before taking them, but also because they consist of very recent official questions and so, a fortiori, will correspond most closely to the upcoming official exam.

if you took the actual old powerprep tests, then get thee to a mba.commery between now and saturday and take the two GMATPrep practice tests. those will give you a fairly accurate idea where you stand.

good luck!