Getting accepted in spite of missing grades.

Hey,
So I got an offer from York for politics and international relations starting September 2015 with an AAB offer. I accepted because I felt like this was easily achievable because I was doing well in all my subjects and I had done well the previous year (an A in maths and a high B in politics). But after 2 messed up exams I'm not sure I'll get ABB :/ if I'm lucky I might end up with 2 As and a C but that is unlikely. How flexible is York on this course? York's the uni I've had my eye on for a few years now so if I couldn't get in it'd destroy me. At the moment I think its more likely I'll get ABC (A - sociology, B - Politics, and C - Maths.)