I may be misunderstanding, but are you saying that you will have have 2 A Level qualifications? You will need 3 to appply for uni. Also, from my experience, unis aren't so bothered about ASs. They're great to have but not to the detriment of your A Level subjects / qualifications. I hope that makes sense.
Another thought: Have you considered doing an EPQ in one of the subjects that you would like to do an AS in? That way, you could still explore your interests in that subject, and unis value EPQs more than ASs, I believe, when they are deciding upon your offers