Danny
I don't want to get too deep into this, partly because it's been covered many times before on Wannabes, and partly because it's something that you should discuss in great detail with those who know you and your abilities best. That is, your teacher/tutor and your parents.
Don't make any assumptions about what qualifications are required by airlines - you'll probably be wrong! The only qualification required by a 747 pilot is an ATPL with a B747 type rating. The few but various sponsorships available have differing qualification requirements, but most will accept 5 GCSEs (which should include maths, a science and English) all at grade 'C' or above, and 2 A-levels - usually unspecified. A degree will always help, but there are no preferred subjects.
As Ian and Loretta say above, the most important thing is to do subjects you enjoy to the best of your ability. If you are missing any of the required GCSEs, sort that out now!