Today i appeared for my GMAT exam and scored the lowest ever - 510( q-49 , v-12

)
When i started preparation four months ago i had given GMAT prep and my score was 570( q-47 v-26).
I worked hard on RC and SC, i was good at CR right from the beginning( although i lacked in speed that i compensated later on).My
MGMAT and GMAT prep scores are as follows -
1)
MGMAT 1 - 600(q-49 v 25)- 15th aug2010
2)
MGMAT 2 - 640(q-51 v29) - 3rd sept 2010
3)
MGMAT 3 - 630( Q-50 V28) - 9th sept 2010
4)
MGMAT 4 - 640( Q-48 V-30) - 3rd oct 2010
GMAT prep Version1 - test 2 repeat- 750( q-50 v- 41 ...7 days before actual GMAT... almost 10 questions were repeated first time i had given this test in sept 2010 and got 680)
GMAT Prep Version2 - test 2 - 660( q -50 v-29).. 3-4 questions of CR were repeated from OG-12th edition,after giving this test i was very confident because in verbal i had got 7 questions incorrect in a row, and this was very much avoidable.
I had given GMAT prep version 1 3-4 times score varied from 680-750.
After doing hard work of 4 months if result is like this i really don't know what to do next
Still i don't believe that v-12 on the real GMAT is my score!!
Need suggestions......
Kindly help me out!!