I don't think anyone can say.
It is a one-off random sample.
There is no way of telling how you will cope psychologically, nor how many standard deviations away from your true score you will be on the day.
You should be as relaxed, healthy and happy as possible.
After that, you should do as much as work as will help you on your weakest areas.
You cannot easily coast the GMAT, or try and beat it, or try and do just enough work to get a mark.
I don't know how accurate the Kaplan
marking is - I have never tried it, and people here disagree.
Try the Powerprep tests for a better guide.