GMAT Strategy

Hi All,
I've been using the Online Kaplan Prep kit to study for my exam.
In the past few weeks, I've taken about 4 Kaplan Cat exams online and have been scoring between 570-590 on these exams.
I just used the score calculator from https://gmatclub.com/gmat-score-calculator/ to get an idea of my actual GMAT score and noticed that this relates for about 660-680. I have read in a few places that the Kaplan exams are harder than the MGMAT and other CATs out there.
I'd like to know if the Kaplan Prep CATs on this calculator the same ones as the online version of the tests that I've taken? Or are these CATs based on some other Kaplan tests found with the Premier Kaplan material perhaps?
Basically I am trying to figure out if my scores are skewed because of the fact that its kaplan.
My ideal score is about 650 and my exam is in a month.
Thanks in advance!

why not try taking a GMAT prep exam to see how you might do? Its the closest thing to the real thing.

mba.com