You do not have to submit your UCAS application for Medicine until October - and for other courses, January 2004.
That gives you time to work your socks off to raise your grades. Go and see your subject teachers now, and ask for their help - what can you do over the summer that will help, how can you show them that you are determined to work harder/better to raise your grades etc, and if you do this, and show that you are working at a higher level, they may reconsider your predicted grades. Go and see them on Monday.