I am not sure where you exactly live and where do you want to go to university but usually you either decide to study engineering (and there are different kinds of engineering) or you decide to go in Mathematics or physics.
Note that whatever kind of engineering you choose at the university, you will need to take basic classes in physics and basic classes in mathematics (and sometimes more advanced).
Different kinds of engineering: mechanical, civil, electrical, computer, aerospace, genetic, etc...
I am not an engineer myself but it depends on what kind of work you would like to do in the future you will choose what kind.
I suggest that you speak to academic advisors in engineering.
I am a mathematician. If you have a passion to mathematics. I encourage you to at least start with a minor in mathematics whatever you do in Sciences/engineering.
Mathematics can be studied very purely. You study different theories. But also you can study applied mathematics and this field is growing very much. Mathematics is used in different fields of science. But not only science, Mathematics is used in business and even arts!
Interesting theories in mathematics: Real and Complex analysis, Differential equations, number theory, dynamical systems, differential geometry, etc..
If you choose physics then you will be studying advanced mechanics (which most probably you started by studying Newton's laws in high school). You will study about the theory of electromagnetism. You will study thermal physics, nuclear physics and as you advance in your degree you will look at quantum mechanics and theory of relativity. Note that once you reached an advanced level of physics there will be a lot of Mathematics that is involved.
I hope this helps
