Like I said, don't worry about timing yet until you are comfortable with math. When you actually start timing yourself you will be less likely to guess on questions that you are able to do.
I just refreshed my memory with the kaplan blue book section and some random online tutorials on stuff I forgot (since I have been using a calculator for the last 4 years). I then tried taking the Kaplan test while timing myself and got a 14 and barely got to question 20. I then did the DAT destoryer, not Math Destroyer, without worrying about time then took a test with my strategy and got 18, now I'm gettin 18-20 on each test I take. I did not time myself until I took a full length test on Topscore. Since you have the Math Destroyer then you can time yourself on some of those tests. Maybe like practice with the first 5 tests then time yourself with the last 5. Taking full length tests is extra practive as well. You will notice a huge improvement and I think doing this you will be fine, good luck.