I too had the same problem when I was preparing for the test, because I did it untimed and got about 32~34 out of 40 questions on average I'd say.
I probably took a lot more than the allotted time and I thought there was no point in trying to finish it on time if the only way to finish on time is by guessing the last 10 or so questions.
Just try as many problems as you possibly can and like many people and myself have realized, there is a pattern of problems they give you.
On the real test, the math problems aren't as complicated as they are on the destroyer or on the bootcamp, so it's likely that you will be pleasantly surprised.
I really dreaded QR section because I took calc 1 and 2 about 10 years ago and algebra and geometry probably 15 years ago, but I trudged through the destroyer math book and ended up getting 23, even after guessing for about 3~4 problems at the end because of time restraint.
Oh BTW, if you see a problem that you cannot immediately answer, SKIP it and come back. (this may sound like a cliche now that it's mentioned everywhere, but this is really important because you cannot use more than a minute for any question on there and if you are stuck on one problem for 5 minutes, then 20+ score is a bye-bye)