imo failing your mocks isn't that bad - the worst thing that could happen is: getting put down into a lower set or getting extra lessons.
As someone who completed their gcses last year; failing your mocks isn't bad at all. I got a D in my french mock and **nothing happened - and I ended up with a B at the end (detested french!!!) IF ANYTHING FAIL THEM SO IT MOTIVATES YOU TO DO WELL IN THE REAL EXAMINATIONS (teachers actually put extra attention on you if you fail because it looks bad on them l o l so failing mocks isn't that bad) :-)
**most people in my french class got D's - B's no A/A*'s this made my teacher realise that he had to change his resources or teaching style. he looked at what most of us got wrong overall and helped us with that and then 78573472304 past papers. at results day 2 students in my class failed (they both got D's) and 7 students got A/A*'s and the rest C/B's (16 people in my class)