One issue is that Subject Tests are based on first year HS course-word.
Physics, for example, covers everything you probably had in an initial physics class. Physics C Mechanics is deep dive in Mechanics, way deeper than the Subject Test, but nothing in the other areas of the test. Similarly, Calc BC is way past the topics on either math test.
My D, for example, will be done with three of them as a Sophomore.
Sounds like US History May be your best option. Review the test description to see how it aligns with your coursework. My D had to do a little self-study for Math 2 and Chemistry.
Fwiw, Lit Subject Test and SAT EBRW are completely different. Narrative voice, imagery, figurative language, connotation, etc. Not grammar and word usage.