How to do well on the math SAT if you struggle with math?

As the other answers said, practice is the only way to get better at SAT math. The best way for me to practice was using Khan Academy's personalized SAT math practice. It covers all the different topics on the SAT math section, gives you timed mini sections, and even has full practice tests available. If you've taken any PSATs, you can link your CollegeBoard account to Khan Academy and it'll look at the questions you got wrong and tell you how you can improve. While I am a more math minded person, this helped me a lot, where in my PSATs I would score about 100+ points off in the math section, I was able to score a 780/800 in the math section of the actual SAT. The best thing about this program is that it's completely free.

Honestly, just practice. Find practice tests or SAT books that have explanations. Do a practice test and correct your answers. When you are done, FIND OUT WHERE YOU WENT WRONG!!! This is super important! Find explanations of how to solve the problem and see where you went wrong. Taking this time ensures that you will learn from your mistakes and make them less. Also if you are a visual learner I highly suggest drawing pictures next to the problem so you can visualize it!! Good luck :)

It's perfectly normal to take Algebra 1 in 9th grade, and to complete SAT math material in 11th grade. That's true for the vast majority of students, just not for the small minority aiming for really selective STEM institutions. Don't worry about comparing yourself with those people; you're coming from a fundamentally different direction, and if you're very advanced in the humanities, it's fine if you go through a normal high school math curriculum (i.e. Algebra 1/2, Geometry, Precalc).

My suggestion is to just practice, a lot. There aren't really many shortcuts to doing well on these exams beyond taking a lot of practice tests. Obviously you can't really do these yet—since you haven't learned a lot of the material—but you can try different sections or just practice bit by bit over the next year or so. Also, take the PSAT this fall if you have the opportunity; there are no stakes to it at all as a sophomore, and it'll give you an idea of what you might need to work on for the real thing.