“Overthinking” is probably the correct word. You are doing really well.
Your GPA is excellent. You have one single B in your entire high school career!
You are doing very well in math. You are already taking calculus as a senior. I did not take calculus until my freshman year in university. This did not stop me from being a math major at MIT. The main point in math is to get a solid basis in the math that you have taken (such as an A in honors algebra and another A in precalculus).
The University of Michigan is a really good university. The graduates from U.Michigan that I have known have been exceptional. However, Michigan has 29,000 undergraduate students. Just being academically excellent and being in-state will give you very good chances of admissions there. If there are a small handful of students in your high school who are just as strong and one class ahead in math, they are likely to get accepted also. There is room for U.Michigan to accept several of you from the same high school.
Really you just need to get a good night’s sleep on a regular basis, keep doing as well as you have been doing in high school (which is great), participate in the ECs that matter to you, treat people fairly, and make sure that you apply to some safeties.