GCSE Computer Science Level?

I really want to take Computer Science as an A-Level in the UK but since I never did it for GCSE, I wanted to know if this Python course would teach me everything I need to catch up?

probably not, it teaches mostly about the language, not any CS theory above that

you would need to have a syllabus to know that

maybe check Khan Academy

AQA Specification for CS GCSE

CS50 is likely to cover most things. Khan Academy, as mentioned. FCC’s Python and JS curriculum probably covers most [practical] stuff.