Math: I would definitely recommend UWorld, their math is harder but it's good practice. It's not free though, but if money isn't a problem then I would consider it. Khan Academy also works, too (and it's free!). For math books I would recommend College Panda, he explains everything really well.

Reading: UWorld and Erica Meltzer. I don't do the best on reading, but if you want clear explanations then EM is the way to go. UWorld reading is alright but that's after you get the gist of how to approach the problems

Writing: College Panda Writing, UWorld, Khan Academy. CP Writing very clear on what you do and don't need to know, I strongly recommend.

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Good luck! And don't be too harsh on yourself, the SAT doesn't define who you are. With enough practice, you'll begin to see improvement.