DO NOT WORRY!
On average, 60 marks are needed on the higher tier for a C grade, however, in some years it has varied. To me, I considered this examination serious to be a bit easier than last years. However, last years boundaries were high and this was abnormal and this meant there was a high amount of students who had to resit. This year, i predict it will be 62 for a C as todays paper was a really weird paper, it seemed a bit too random.
hope this helps