600 blah...what I think I did wrong

I sat for my GMAT yesterday and received a 600 . To look on the bright side it's better than where I could have been and now I have a lot more to learn.

My journey began about a month ago. At the end of January, I sat for my first practice test: 460 (felt disgusted). I began researching if the GMAT was going to be easy to learn...found out it wasn't. I browsed through GMATCLUB and found some great articles, debriefs and book reviews. I got the ManhattanGMAT books and the OG 12 and was ready to tackle the GMAT down. I went through number properties which was great! I took down notes, solved all of the problems, and put anything I couldn't remember down on a flash card. I read on here that SC was easy to learn so I tackled it in the same manner. However, as time started winding down, I skimmed through the rest of the books and the Powerscore critical reasoning bible, just jotting down notes, not doing many problems or completely understanding. With the limited time I had, I didn't review my notes/flashcards too much. I think this is where I may have started gone wrong.

In addition, I didn't do all of the OG problems, while I'm sure its not necessary to do them all, I completed the entire set for sentence correction and saw that part of my arsenal shot through the roof. I only did about 65% PS, 45% DS, 40% CR, and 50% RC. I reviewed all of my problems, both right and wrong, but I don't know if the concepts stuck with me. In addition, I forgot about gmatclub until my last week of study, and was late in finding a lot of great math articles and tests. However, my low score was somewhat surprising given my scores leading up to the exam. There was A LOT of fluctuation.
EDIT: I used an error log and notes such as spidey's sc notes, slingfox notes, target 760 notes, chineseburned AWA guide, etc.

GMATPREP 1 (end of February): 460 (no practice done)
Manhattan(03/11/11): 590 (was happy I was getting better, but upset I didn't get past 600)
Manhattan(03/18/11): 650!!!!
GMAT Prep2 (03/20/11): 580 (wtf??)
GMAT Prep1 again (03/21/11): 680 (I think 9 questions I got were the same)

I'm planning to give myself another 2-4 months to study. I want to post 700 results before I take the actual exam. Can anyone offer any advice given my condition?

i have:
OG 12
All of the manhattangmat books excluding math foundations
Powerscore critical reasoning (my weakest section)

Thanks for any tips and I hope I can post a 700 result soon!