While others have pointed out that many schools, MIT included, say they’ll “accept” either Math Subject Test, and concluded that it doesn’t matter, I stand by my opinion that a very good Math 2 score will be much more attractive than a very good Math 1 score. This would apply most anywhere, for any major, though obviously more significantly for STEM majors/top schools.
If you’ve taken Pre-calc, going back to remember/study Math 1 topics may even be harder/result in a lower score. College Board itself says
“If you have taken trigonometry or elementary functions (precalculus) or both, received grades of B or better in these courses, and are comfortable knowing when and how to use a scientific or graphing calculator, you should select the Level 2 test. If you are sufficiently prepared to take Level 2, but elect to take Level 1 in hopes of receiving a higher score, you may not do as well as you expect. You may want to consider taking the test that covers the topics you learned most recently, since the material will be fresh in your mind.”
I wouldn’t let the effort/cost? of returning a book be your deciding factor.