Cancelled Score! Need Quant Help!

All,

I've only posted a few times but I swore I'd post whatever happened with the GMAT here in the hopes that others would somehow benefit. In short- I definitely know I need to step up my quant practice.

Full disclaimer: I took Veritas prep and also did private tutoring. In addition to that, I bought the 11th edition OG and the OG supplemental review books. In practice, I have been scoring in the 99th percentile in verbal, and quant...well, around the 60th percentile.

I took the exam this morning: essays were great, then quant was a runaway train that got way way way away from me...verbal was great. I cancelled because I know I didn't make the mark in quant, and that's what I need to show the adcoms I can do.

My quant experience:
I ended up having 10 minutes left for 10 problems. This is not good! Also, I thought that a lot of the questions really really tested your theoretical knowledge of math and arithmetic, not just knowledge of how to do practice problems. I was expecting a lot more algebra, and unfortunately I didn't see it.

On the Saturday before the test, I took a sample GMATPrep, and got a 47 in quant, my highest score ever. I thought, I'm set, all my prep has paid off. Well...not so much.

If anyone could answer this question for me, I'd really appreciate it: when you go through the OG, and you "understand why a problem is wrong," is there some deeper level of understanding to take away besides, well, if I saw that again, I'd know how to solve it? How do you get there? I can see that that's what I need to do to score 80th percentile+, but I'm not sure how to go about it. Or in general, how do some of you do it?!