I would try to prepare and get decent SAT I or ACT scores. If you are applying to good schools, I would take and submit SAT IIs: you should get good scores on those if you are studying for A-levels. If you can’t get good scores on the SAT or ACT, then look for schools that will just take your A-levels. Schools in the US are used to looking at grades and SATs. You don’t have grades in the US sense, so it is better to give them some of what they are used to loking at.