How hard is Maths at university level?

I scored very poorly in my GCSE's, getting only B's and C's, and no A's or A*'s (but I was ill at hospital the month before exams). But at A-Level, I did very good, and got ABB- with A in MATHS (and B's in Accounting and Economics)!! I love Maths. Anyway I'm going to university of Sheffield in September to study Accounting & Finance and Maths (dual honours). But I'm scared of the Maths half of the degree. Will I find it so hard that it will make me consider changing course, because this has happened to some of my friends, and it's starting to deter me from my favourite subject?