There was a huge mix-up in my GCSE Geography grade.
My A* mark of 55 in the coursework was sent off and AQA marked it down as a B grade. I emailed my teacher about it, and he said that it is quite possible that AQA have messed it up, and he is sending everyone's exams off for a remark as loads of people have questioned him about it.
I say you ask your teacher, see what they can do, and go from there.
For the record, I got a B in my iGCSE English Language, when I was predicted an A*. We're all unlucky people.