Don't worry too much! Everyone else in my class (11, I think - can't count ) found it hard - that includes another girl going to Cambridge for maths, and others for different subjects. I suspect grade boundaries will be low.
The paper was certainly unusual. The 11 mark part was a surprise in which I admit that I crossed out four or five lines of working to find a simpler way.
Good luck with your other exams!
ahh that's good (well not good but yeah ) I'm hoping for around the 45 mark I think... And thanks, good luck with yours too!