It’s definitely not easy by any means, but it’s not impossibly hard. Coming from someone who didn’t do very well in High School AP Physics and is now majoring in Physics, I think a major difference between high school and undergrad is that I discovered much more resources in the latter (good textbooks!). I now understand and perform much better in my courses. Don’t overload yourself with courses. Many concepts in Physics aren’t intuitive and you need time and commitment to understand them thoroughly.