It is funny that we are complaining about being "stuck" at a relatively decent score
I would have killed to be at this score a few months ago.
You bring up a good topic… what to do when you have made a mistake. I did a problem earlier that used the compound interest formula and for some reason i did 11^2 = 111. Once you get to the answer choices and not seeing your answer is a really bad feeling. I went back and started from scratch and screwed up again (same mistake). I had so much time invested in the problem I checked everything and found my mistake. Of course, on a real test this is probably not practical. You then have to deal with the anxiety of wondering if you got the formula wrong, or whatever else went wrong. On a tougher problem, I usually look for any errors (of course they are always hard to find under a time constraint), and then just pick the answer closest to mine. On a simple problem that you know you should get, it is really hard to just guess and keep going.