You're highly unlikely to be able to stay for free at a college to re-take, but you can study at home, paying a tutor if necessary, and find somewhere to accept you as a private candidate to re-sit next Summer. Your current college is likely to be the cheapest place if they will have you back but they may not. The entry fee at the exam board for an A level is £90-£130 but expect to pay a fair bit more than that for the centres admin, invigilation etc. The entry deadline at the exam board is 21 February but you should aim to have sorted a centre before Christmas and finalised everything in January.
If any of your subjects have assessed practicals or NEA you can carry forward the marks for that - which is handy as it is extremely difficult to find anywhere to re-sit that as a private candidate.