I signed up for 2 SAT subject tests, can I just take one of them?

My mom insisted that I sign up for both Math I and Math II for some reason, though I (and many others) think that, of the two, Math I isn't really necessary. I think she was convinced of my view after talking with some of my cousins, and I just don't plan on bothering taking Math I as I really see no point. Can I remove Math I somehow, or on test day just not take it?

You can absolutely just not take the Math I SAT subject test on test day. If you don't care about the refund, then it's as simple as not showing up to take the test (for that specific test session - you should still go to the Math II test session). It won't show up on your record - as far as College Board is concerned, if you paid, then it's up to you to show up to the test. Not taking the test effectively cancels the test registration.

If you want to try for a refund, you can try contacting Customer Service. Be aware, however, that you have to do this at least 5 days before your testing date, and that you'll get (at most) $10 of your registration fee back. Trying for a refund is mainly useful if you also ordered Question and Answer Service or Student Answer Service for the test you're canceling - you'll be refunded the QAS or SAS fee in full if you cancel >5 days before the test date.

If your mom is still wavering about having you take the SAT Math 1 subject test, we have a great article about the differences between the tests (and who should take which) in this article. There are also a couple of other ExpertHub posts about SAT Math I vs Math II that you might find useful.