If you’re already scoring that high, I agree that it’s probably just stupid mistakes. If you have any time left after finishing, you should definitely look over all your answers one more time, no matter how easy you thought it was. I’ve found this to work really well while taking math tests in particular since it’s really easy to either mess up on simple calculations or to forget to do everything the question tells you to do and looking over the questions again could help you spot an error like that.