as long as your AS' are good and you go for good experience then I can't imagine why you won't get considered. You can't change them now, so focus on doing well with AS, do as much experience as possible, and aim for your goals. Study hard, work hard, but also just know that everything works out fine in the end. Just do your best and learn from your mistake - GCSEs really aren't the be all and end all. As long as your AS are better you should be fine.