BTW, with a top IB score and a year of UK uni, you’re almost guaranteed to get advanced standing (so starting as a sophomore). But that also means that many of the classes in your remaining 3 years will be in the major you choose (though you would still have time to choose).
IMO, your chances of getting in to some “top 50” American college (by which I mean an American school that can claim to be ranked in the top 50 on some USNews ranking) are good if you can be full-pay, though they may not be as prestigious worldwide as the UK uni you will be going to.
I say that because a top IB score makes GPA irrelevant (and SAT/ACT scores somewhat irrelevant too).