Some of you people are being totally ridiculous. An A might be a "very good" grade, but it's not an "excellent" grade, and if you can't get an A* at GCSE, especially in such a subjective subject, what are your chances of pursuing it to university level? Of course the OP knows she can do it and her teachers seem to too. But the university interviewers might not know that, and especially with AS exams having no equivalent A* grade, and very few universities seeing your individual module scores, they might think she was only a "mediocre A" candidate. Now this for many people might be bloody good, but for university level, it really doesn't cut it.
I know people who couldn't get GCSEs if they tried. But their ambitions are to get jobs, not to go to university. Right now I couldn't do "manual" jobs if I tried, because I'm not that sort of person and have little experience. If you have big plans to go to uni and this late on those plans are in any way jeapordised or threatened because you or someone else thinks you're not quite the appropriate student for the course they thought you were, it can be quite distressing. Try being considerate, please.
MisterE, you talk crap. How does an A at AS level override the exact same grade at GCSE? That doesn't show improvement or excellence at all, just an accumulation of knowledge and a bit of experience. There's no way you can tell between a low and a high A grade at AS, although there is at GCSE with the introduction of A* a few years back now. If someone gets an A at AS and an A* at GCSE, it's fair to assume they're a better candidate than someone who gets A at AS and A at GCSE, because the latter looks like they may only have a low A at AS and the former may well have a higher one, based entirely on the GCSE grades. Don't be so dismissive.
Chriztina27: despite the advice I've given above, I would recommend you didn't retake. If nothing else, the texts won't all be the same, which would just be a huge accumulation of work... and then you'd have all the coursework to retake, since, unlike A-level modules, you can't carry your coursework marks forward and just retake the exams. Leave it and explain it during the interview, but don't let it concern you too much. What's done is done, and unless you really did do badly and got a C or something, I wouldn't bother with the huge extra workload.
On the other hand, I'm sure you could resubmit your coursework as fresh pieces (assuming you saved them on the computer or something) and study the same texts... that might, after all, not be so bad. I wouldn't recommend it but if you have the time and it really means that much to you, go for it. Your call. It's not a terrible idea.