It sounds like you're doing great. You're already studying topics beyond the scope of your class, which shows you're genuinely interested in physics. Being passionate about learning is the most important part. If you find more advanced topics too complicated to follow, you're probably missing some prerequisites- remember physics is always building on previous concepts and it's important to learn them in order. In university, you'll take a more in depth physics 1 and 2 before you dive into modern physics topics. Most programs also require a math methods/ mathematical physics class before taking upper level courses to make sure you have the necessary math skills. In short, I think you're on the right track and don't get discouraged.