If you love math and science, I would say start by getting involved in extracurriculars in those areas. See if you can get involved in research, maybe at a local university, and explore different specializations within the fields you enjoy to start narrowing down your search.
I think that a lot of (if not most) people who go into college with a major in mind change it during their time there, so I would honestly recommend that you focus less on finding a specific major, and more on finding interests and career paths you like, regardless of your major.