GMAT Strategy

I am aware of the community rules and I think I did some search to find blogs where people have scored low gmat score and pulled it up.

Basically I took a test August and scored a 550 (43Q, 25V) clearly my verbal was really bad. I decided to take ManHattan GMAT class and it was pretty good. I was scoring 620-670 range in MGMAT. But was scoring about 610 in PowerPrep. I studied intensively for those 2 months and gave the test again in Nov but scored a disappointing 570 (49Q, 20V) again.... It was a big shock to me, what did I do wrong.. I thought I had prepared to get atleast a 600, the worst case.

I am not sure what I did wrong. I need advise on how should I approach now. I have done OG-11, OG-Verbal, OG-Quant, Princeton, Kaplan. It is a little frustrated but I am determined to score 650+

1. What should my strategy be from now on? I have ordered OG-10 and thinking of studying that but I know my weakness remains in SC and CR

2. Also, I have been working on my application for the 2nd round, considering DUKE and UNC as my first choice. If I give my GMAT again would the school consider my score a month after the 2nd round deadline (1st week of Jan). Plan to give end of January

I would like to give my GMAT mid-Jan but I am only getting dates for the end of January. Do you guys think I should give it before, (problems getting dates in the evening, since I am not a morning person would try to avoid 8am tests)

Please help. Thanks in advance