Hi, I also want to major in Computer Science so I think I can give you some suggestions / advice.
If your school offers IB Comp Sci (HL/SL), I would definitely recommend taking it. It'll give you a good feel of how college Comp Sci courses are like. Unfortunately, my school didn't provide this opportunity
I strongly recommend Math HL, as the majority Comp Sci courses involve a lot of math. As nomenclature has said before, it will help you with things such as calculus, vectors which are key in university comp sci courses.
I would recommend taking two science courses if you are seriously considering Comp Sci, or any science-related field for that matter. I'd suggest taking IB Physics (I don't know if you would like it though) as it also involves problem solving with Math. Also IB Physics offers an Engineering options course in your senior year that could tie in with Comp Sci content (I dont know about this for sure, however).
Again, these are just recommendations, and the ultimate course selection is up to you.