“I prefer quantum physics, mechanical physics is too difficult”
When you get into quantum physics at a demanding university, it gets difficult. At least for me (as a math major) mechanical physics was easy, special relativity was a bit difficult but definitely doable, and quantum physics was tough. Quantum physics was the last university physics course that I took unless you count thermodynamics (which was considered a chemistry course where I was).
You are young, and have a lot of time to sort this out. I would not retake a B in physics. I would try to stay well ahead in your math courses. Math is a major basis for physics (which is why I liked physics better than other sciences).
Being in-state at the University of Michigan should help your chances, and make it relatively affordable for you. It is a great university which is very well respected by those of us who live elsewhere. I might be tempted to throw in an additional application to MSU as a safety.
“Perdue” of course is very good chicken. “Purdue” is a very good university.