You don't have a hope of a sporting scholarship unless you are amazing (which means playing at a national / international level).
Not many American universities offer full scholarships to international students. Only the best (and hardest to get into) universities like Harvard, Yale and Princeton offer really good financial aid to international students, and you need to be very smart and have a tonne of extracurricular activities to stand a chance. They're looking for exceptional students, e.g. people who invented a popular app, written a book or started a charity in their spare time whilst maintaining excellent grades.
It is also worth saying that you have to be pretty poor to qualify for a full scholarship even if you get into the likes of Harvard. They will assess your combined family income, savings, and assets to determine what you can afford to pay. If both your parents work then it is unlikely you will qualify for a full scholarship.
In short, I think the US is a bit of a pipe dream for most British students. I think you should focus on your AS levels for now, do some extracurricular activities and reassess your US ambitions in 6 months. It is certainly way too early to be thinking about the application process.