no offence but take a look on some of the college forums the amount of ECs that Stanford applicants have. They all have at least 1 SKILL, they have at least 1 ORGANISATION, in which they have decent experience, they all have at least 1 SPORT at which they are at a decent level, and all have VOLUNTEERING experience. This is the bread and butter of your ECs, so I would suggest a vast widening of experiences. Entering a few essay/academic competitions wouldnt hurt either.
And by the way, I dont see the point of doing IB and AS personally - but then again, i wouldnt be willing to take a year out for that particular option. Your GCSEs are obviously well below the GPA of Stanford, but I suppose if you did pull off incredible AS and IB scores as you are describing, it might be cancelled out.
Good luck
EDIT: Oh and by the way, Im in lower 6th and also planning to apply to Stanford for my first choice