I’m only just finished Geometry and I’m going to be a junior soon. I’ll be taking the PSAT this October. I’m mad that I’ve only just finished Geometry and if there was some accelerated math course I could take, I’d do it in a heart beat. I know it won’t do me any good to be mad however. The math on the PSAT is way above my grade level, we’re talking 2 years. I do fine on the English portions and I know I can score very well with a little bit of studying but I don’t want to study hard for this if I can study for the ACT instead. I know that even though I study insanely, I won’t pass because I’m way too behind in math but I feel like if I don’t study, it’s my fault that I didn’t pass. What should I do?
If you think you can get the national merit, yes. If not, no, it isn’t really necessary, but it can’t hurt.
But don’t feel like studying for this would be a waste of time. It would indirectly (and directly) be studying for the ACT as well. Enhancing your math skills and reading comprehension, regardless of the test, is going to help your standardized test scores for sure. Definitely don’t kill yourself over it, but don’t do what I did either (not study at all because you assume you won’t get it and then end up a few points away from what’s projected to be the national merit cutoff for you state)…ah well, at least I’ll likely get a commended.
Also, don’t feel weighed down by math. Since I took calc last year, all the past math kinda blurs together for me, but I think the majority of standardized testing tests algebra and geometry…not sure how much of that algebra is algebra 1 vs. algebra 2, but precalc is very little of the tests (some conics and matrices for ACT, but I believe that’s it). Focus on filling some of those gaps of knowledge, increase your reading comprehension, and you’ll be golden! Good luck 
Thank you very much! @berkdork do you mind me asking if when you were a junior and you took the PSAT, were you ahead in math?
Take the free practice test, available from the College Board’s website (you can easily google it). If you perform within spitting distance of National Merit Semifinalist qualification, then it’s worth it to study.
The state you are in will also have a lot to do with how competitive you are for National Merit recognition.