Folks, I am really upset

because I did not do well in my actual GMAT that I took today. Clearly I was in no position to get a good score as I did not start my math section very well.
These are the following reasons due to which I did not do well
1. I did not manage my time properly at all.
2. Permutations and Combinations was really bad (not the problems but the way I was trying to solve them and I got totally nervous and did not get it right).
3. My verbal section, I thought was going good but I was surprised that I did even worse than my math section.
So In general a multitude of problems!!!! I desperately need your help GMAT Club members. I still am planning to apply for the weekend MBA program this year and I am still planning to take another shot in the first week of March. What is the best way to start preparing for the exam?
How good is the OG book that I have been reading about?
Thanks,