I was lazy during my year 12 too but i just slaved throughout my yr13, resat my C1,C2 and D1 Modules in year 13 (found the three so much easier 100 ums on c1 and c2 so i was really pleased) From that i was pretty confident that my revision was working and finished my exams. I didn't initially get the offer for a Russel group (I was aiming for Manchester) but when the time comes to pick your offers theres a thing called adjustment were u can change the course you are going to go for that is if you get the grades, if not you can always apply for the foundation year version of the course if you are thinking of a resit year.