What are my chances of entering top universities?

I’m an international student (non-US), currently doing my GSCEs, and will be doing my AS levels next year. My question is how good of a result should I get, in order to have a good chance of entering some of the top universities in the US. Are there anything else that I should know, to maximize my chances of being admitted into these universities? My choices of universities include UCLA, Boston University, Northwestern University, anything in the top 100 rankings. My academic performance is above average, the only problem is that I have zero achievement in extra-curricular activities, which sounds like a super bad thing. Are my chances still good if I have good test results but awful EC? If they’re bad, what can I do to improve them and increase my chances of being admitted?