What high school classes can I take to prepare for physical therapy in college? And what should i do in college as in classes and activities to prepare for my journey?

As far as highschool goes, I would try to take as much anatomy, chemistry, and physics as possible. If your school offers any sports medicine or athletic training courses I would take them as well. As far as extracurricular activities go, I would try to volunteer with your HS sports teams helping the athletic trainer (who will use a lot of similar skills) or in a PT clinic/hospital.

In college, the #1 thing you can do is hoping the pre-physical therapy society immediately and volunteer to help. (I talked about this with a pre med student once before https://www.careervillage.org/questions/47696/what-are-some-study-skills-or-daily-habits-that-really-helped-you-stay-organized-in-college-and-medical-school?page=1#47719 and recommend reading the same book that I mentioned in that post.)

You can also:
-volunteer at therapy conferences
-apply to be a TA for a course related to therapy such an anatomy or Biomechanics
-tutor courses
-help professors complete basic research projects
-apply for jobs as a PT Aide.

P.S. I was planning on studying Physical therapy in graduate school but later decided to become a PT-Assistant instead due to the decreased work stress, cost of tuition, and that it fit better with my career goals (I hope to enter a PhD program after a few years' experience in the field.) I would highly recommend exploring that career thoroughly while in highschool. As an associate's degree, PTA offers a viable alternative to 7 years of college and +$150k of debt.