I think it’s fair to say that your SAT results are not going to mean a dam thing, the important things are your GCSE and A Levels, those little pieces of paper are going to be the things that take you somewhere. But as was said, they are not the be all and end all, however are still important.
With the industry the way it is today, there are only a few jobs out there, and when you apply for them, you are going to want anything that puts you above the rest. Yet you have plenty of time until you can apply to become an airline pilot, so the industry may have recovered and the job scene improved by then.
My suggestion would be, do everything and anything that will put you above the rest, whether this is being a prefect if you go to a sixth form, doing community service (hopefully not compulsory otherwise you are in trouble) learning mentor within your school, duke of Edinburgh etc, basically any extra curricular activities that you will be acknowledged for, you can't go wrong, but most importantly, as has been said, you need the determination, if you have the determination you can do anything.
Only other thing I would say, if you haven't all ready, go and have a trial flight at your local airport, that should give you an indication if you like flying or not.
Best of luck
Dan