I am so highly disappointed

I had taken GMAT 3 years ago and had ended up getting 600 (Q-44,V-29). Again yesterday I took my GMAT (2nd attempt)and ended up with same score 600 (q-47,v-26)
I have been consistently getting scores within the range of 680 to 740 during my last 3 months prep in all the GMATPrep and Manhattan tests.
Yesterday when I saw my score I could not believe the numbers flashing on the screen.
I am totally confused. Unfortunately i am an engineer+IT and belong to the very common pool of applicants and to get to any good school I need to make it to 700+ pool of applicants.
After yesterday's experience I have lost confidence if I can do with the self study and can still take a100 points leap and in third attempt too I'l end up with the same score:(
Plz suggest should I give it another shot, is it okey to have 3 scores? What should be my strategy?
Please guide.