Given that you scored a 680 (Q48 and V35), you clearly have a solid grasp of GMAT quant and verbal. Thus, to gain the 20 points you need, you may consider following a regimen of focused quant and verbal practice, to help find and fix any remaining weak areas.
For example, if you are reviewing Critical Reasoning, be sure that you can practice a large number of questions just from Critical Reasoning: strengthen and weaken the conclusion, resolve the paradox, find the conclusion, must be true, etc.. The results of that practice will help you determine your weak areas within that topic. Once you find and fix your weak areas, then move on to the next verbal topic.
You may follow the same routine for quant. For example, if you are reviewing number properties, be sure that you can practice 50 or more questions just from Number Properties: LCM, GCF, units digit patterns, divisibility, remainders, etc. The results of that practice will help you determine your weak areas within that topic. Once you find and fix your weak areas, then move on to the next quant topic.
If you would like some help determining your quant strengths and weaknesses, I welcome you to take my free
37-question quant diagnostic. After completing the diagnostic, you are provided with a detailed analysis of your proficiency level of GMAT quant topics, as well as an opportunity to discuss your diagnostic results with me or another
TTP instructor/coach.
Once you feel confident that you have fixed any remaining weaknesses, resume taking practice exams. I recommend taking the practice exams from MBA.com; those exams provide the most accurate exam experience and use the most accurate scoring algorithm. Since you have already taken the two free exams you can purchase and take
exam pack 1 and
exam pack 2.
If you have any further questions, feel free to reach out. Good luck!