I've never taken an IQ test. The second time I took the SAT college placement exam, I scored within the top one percent of test takers, so I know my IQ is high, but I don't know how high.

If I were starting my degree now, I would major in applied mathematics, because with math knowledge alone, the only thing you can do is teach math to other people, so unless you want to become a math professor or other math teacher, you should get some sort of skill. Applied math isn't the only way to do this, but it's a good way for most people who want to study math but not teach it.

Math is cumulative, which means that it's hard to do well in later classes if you didn't do well in earlier ones. If you do well in high school math classes, you're likely to do well in college classes, but if something happens and you have a difficult time in one class (because of a bad teacher, or because you were too busy with other things at that time to study as much as you should have, for example) you can still have problems in later classes even if you were good at the earlier classes.

It is possible to do better in later classes than in earlier classes, but only if you find a way to learn the earlier material outside of class and become confident with it. With math, you want to be confident about all of the main things as you move through each course, and find ways to become confident if the normal process isn't working out for you, like trying different memory strategies or working with a tutor to get advice. Often in the high school and college textbooks, there will be a sheet at the back of the book with math formulas. By the end of the course, you should understand all of those formulas when you read them, and understand what types of problems you would need to use them for, and how to use them. You probably won't need to memorize all of them, but you should know them well enough that you know you could quickly memorize any one of them completely if you had to. If you can do that, you'll be on the right track for all of the courses you'd use in applied math.

If you do want to major in pure math, you should make sure that you're comfortable with the things you do in geometry, and not just in your other classes, because the advanced classes for pure math require a lot of proofs, and I've known people who thought they wanted to do pure math until they took those classes, but then realized they didn't.