Hi shubham2312,
Just so I’m clear on your situation, are you saying that you sat for the GMAT previously and scored a 630? And then you recently took an official MBA.com practice exam and scored a 510?
If the summary above is accurate, we need to determine why your GMAT score dropped from a 630 on the actual to a 510 on the practice. Also, a score of 510 indicates that there are holes in your GMAT quant and verbal knowledge that must be addressed, to allow you to increase your score.
When you have been studying, have you been able to achieve linear and targeted learning followed by focused practice? In other words, have you been able to master one topic before moving to the next? If you have not been able to study in this way, you may consider adjusting your study routine and rescheduling your exam for a later date.
When considering a new study routine, you must remember that the difficulty of the GMAT lies in the fact that there are so few questions asked in a given exam, yet those questions come from a huge topic pool. Thus, the best way to get a great GMAT quant score is to have a thorough understanding of all that is tested on the GMAT. To develop such mastery, you should fully concentrate on a particular math topic and then practice that topic until it completely sticks.
For example, if you are learning about Number Properties, you should learn everything possible about that topic: LCM, GCF, units digit patterns, divisibility, remainders, etc. After that, be sure that you practice with a lot of questions (50 or more) just on Number Properties. The results of that practice will help you to determine how well you have truly mastered that topic. Follow a similar routine for other quant topics as well as for verbal.
If you have any further questions, feel free to reach out to me directly. Good luck!