In regards to sports: I did varsity track for one semester of high school and it zapped almost all of my energy. It felt like I was either running, or exhausted from running. My grades absolutely tanked. So for me, doing a sport in college, where the intensity cranks up tenfold, would be out of the question.
There are people though who somehow manage to juggle a sport, a part time job, and a full load of STEM classes while getting all A’s. I wouldn’t count on being one of those rare students, especially not with your GPA on the line.
Regarding Physics: get a copy of Serway’s Physics for Scientists and Engineers. Take fastidious notes, do every third or fourth problem in each chapter. Look at the solutions manual if you need to. Make sure you really understand how to do each problem. If even after looking at the solutions manual you still don’t understand, ask your friends, and then ask the professor during office hours.
When you’re reviewing before an exam, redo the problems that you’ve done. Make sure you still know how to do them. Don’t look at the work you’ve already done. Completely redo each problem.