There's been a couple of threads about this already; it all depends on how everyone else does too. If all the people who have accepted their offers make their grades, then the course will be oversubscribed, and they won't have room to let you in. HOwever, if lots of people miss the grades, they'll have spare places to be given to whoever was closest to achieving the right conditions, ie, if you were 2 marks off the A or something.
I wouldn't worry too much about it now - I'm in exactly the same situation for English Lit, as my Spanish exam went horribly wrong. There's nothing anyone can do until this August, so I'd just enjoy the summer whilst you can!