It sounds simple, but practice tests. Lots of them.
Scoring in the 1500s already indicates that you probably know everything you need to know; there won't be areas in either section where you're entirely missing knowledge that you need to answer questions. And as you said, the difference between a 1520 and a 1560 can also be pretty tiny because the SAT is graded on a quasi-bell curve — so while the difference between a 1000 and a 1050 might be huge, the difference at the end of the scale is often a single-digit number of questions.
Because of that, what you need to do is practice the act of test-taking itself. Make sure you can keep your focus throughout the full time (about 3 hours), and that you can pace yourself effectively through a section (i.e., knowing when to skip a questions and come back to it at the end of a section). Do practice sections and time yourself; create an environment as close to the real thing as you possibly can. At this point, that would likely be your best way to improve your score.
Hi! First off, I think your predicted SAT score is amazing, but I understand that we always want to improve more. I would definitely recommend Khan Academy. If you keep a strong schedule (like spending 30min practicing, 5 times a week), you are guaranteed point gains.
I also heard great things about the SAT Prep Black Book, although I have not tried it out. I read a forum where everyone praised it, so maybe check it out.
To keep this community safe and supportive: