you mention that you could only complete 20-23 Math questions, so does that mean you left the rest of the questions blank??? If so, that will really really hurt your scores
I also like to commend you for your perseverance
I think sometimes what makes a 600 to a 800 test taker might be that the 800 test taker is more cautious of the ETS tricks.... have you tried Kaplan
books? They have the 800 Gmat, which I find it helpful and also practice on the Original Guide that ETS published.
Actually most schools would accept 600 , but if you want to get scholarship, then you may need higher scores....with 600, I believe you are able to be admitted to a pretty good grad school. Perhaps you are can talk to an admission advisor from the school that you want to apply, ask them if 600 GMAT scores is what they expect from an applicant. Grad schools look @ everything too like your work experience, GPA and personal essays...
Well,I hope for the best for you
All the best!