I believe that I'm also in the same boat as you are. I too got 600 in KAPLAN
1st test.(Q-50, V- 30). I committed some silly mistakes and ran out of time for Maths too. In english, I made a mess and I believe that I can improve a lot easily. I'm sure to improve and so not very confident of my final showdown.
I took PP1 from OG long back and scored a 750(without touching quant, DS, RC and CR from OG). My scores in Princeton are between 690 - 720( I took 3 tests). I didn't like Princeton tests as I was not satisfied with some of the answers given by princeton.
I'm worried and so not very confident of taking the date for the exam, even though I might crunch onto the dates in the next 15 - 20 days.
Can somebody please advise?