GMAT Strategy

OK here is the deal. I took 3 tests in the past two weeks. First I took Kaplan free online exam. Got 580 (Q38, V34) Then I took Knewton free exam exactly one week later and got 490. I found math section overwhelmingly difficult (ive ran out of time on Q 21 LOL), and I cant even remember the split anymore but it was high 20's for both sections. Mind you, neither Kaplan nor Knewton have a AWA sections for the CAT's. Ive literally just finished Veritas free practice test with AWA section included and got 620 (Q41 V37). Now, taking Knewton out of the equation, I would have guessed my actual score would be in high 500's right now. BUT, I took Knewton this past sunday, and its only thursday today, so only 3 days later, with some, but not much of studying. So i guess, how do I interprit all the scores, and which one is the most accurate? I guess im just insecure that Kaplan and Veritas are flukes and im actually around 500, which is where I was last summer after studying for two months and then taking 8 months break from GMAT to finish my undergrad... (Taking the test in early Oct and aming 650+)