I don't know exactly how the Kaplan scoring works, but if you're only missing ~8 questions a section on a Kaplan test, you're likely going to do well on the real deal. Kaplan is known to have pretty deflated scores, which I believe is attributed to their "money back guarantee". Scoring over 505 consistently on Kaplan tests seems to correlate with high (>514) scores on the test. There's a guy on Reddit that has derived some sort of magical equation to help predict scores based on practice tests, and his method is impressively accurate. Over presumably dozens of test takers, he's predicted scores within 2 points >70% of the time and within 1 point nearly 50% of the time. The main correlation he has found is that a greater number of FL's yields higher MCAT scores (duh). Also, taking a few Kaplan tests, a test or two from other companies, and the AAMC scored and unscored seems to be a solid strategy.
Basically, I wouldn't worry much about your Kaplan scores (I know it's hard...it gets even harder after test day before scores are released). It seems like you're doing really well on them considering Kaplan is notoriously difficult and deflated. Good luck!