It seems you're aiming to leverage your score for 200 points, but improving 200 points is a pretty hard thing. It would be very likely possible if your entry level skills are fine. It won't take much time if you're familiar with the topics of the school level.
If you're an ordinary student, you need to be familiar with the basics first and then start practicing the tests which are alike College Board's real SAT Subject Test.
You should practice at least 100 full-length SAT tests to make yourself highly familiar with the SAT Subject Tests.
So I suggest you take the SAT sample papers which are released by the College Board.
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