If you failed so bad that you believed redoing them wouldnt be of a huge advantage but still want to aspirations of going to university. You could always go college and do a Btec course and then go to uni. Its longer and it wont guarrentee you oxbridge material but its a decent avenue
It's not something I think about too much as unfortunately a reasonable academic record is all I have going for me in this world; noob at guitar and no real business brain that I know of.