Based on the results of your practice exam, I would recommend a full review of the
MGMAT SC materials. The rules are hard to remember when you are studying consistently - over time you will definitely forget them. Since you've been through the material already, your study should go faster this time through. You might also consider the
MGMAT Foundations of Verbal Strategy Guide along with your SC guide (
https://www.manhattangmat.com/storeitems ... ItemID=596). The Foundations book will give you an excellent grasp of all the basic principles, making your study in the SC Guide much more productive.
I must admit that I don't agree with your strategy of focusing on getting the first 20 problems correct. Your focus should be on getting every problem correct that is at or below your ability level (and giving yourself a fighting chance at the harder problems). By placing a majority of you focus on the early problems, you are forcing yourself to miss "easy" problems later in the exam.
Here is an abbreviated table of a "mock exam" showing what I mean by missing "easy" problems later on when you try to optimize the first 20 questions (Q=Question, C=Correct, D=Difficulty):
Q C D
1 Y 50%
5 Y 80%
10 N 90%
15 Y 75%
20 Y 80%
25 N 75%
30 Y 70%
35 N 60%
40 N 50%
Notice that this fake test taker is capable of getting 75-80% difficulty questions correct, but because of poor time allocation he/she is missing 50% level questions towards the end. The test is adaptive and is intepreting your overall score based on your answers relative to question difficulty level - missing a 50% level question is more damaging to your score than missing a 75% level question. If you want to maximize your score, allocate your time so that you can be correct on all questions you are capable of getting right. Guess selectively throughout the exam to keep yourself on pace - don't slide towards the end!
KW