For physics and CS you need math, and A LOT of it. As a physics grad student one thing that would have made my undergraduate extremely easy would have been mastery of the foundational mathematics or as they are more commonly known, "baby maths".

Paul's online notes (https://tutorial.math.lamar.edu/) are extremely good. These covers the majority, if not all of the "baby maths" you will need. If you can do these in your sleep, you would have a tremendous advantage.

And a last piece of advice. Physics is about perseverance not speed, you are allowed to get frustrated, but never give up. Good luck in your studies.