“I’m just bad at math” is a label you stuck on in fifth grade and never checked again.

Somewhere back there you had a hard year, a teacher who moved fast, or a test that went badly, and you filed it as a fact about yourself. The label then did most of the work. You stopped trying as hard in that subject, which produced more evidence, which made the label feel earned. It described one stretch of time, not a permanent setting.

Take one subject you have written yourself off in and give it a fair two weeks. Ask for help early instead of at the test. Whatever happens, you will at least be judging yourself on current information.