How can I convince my teachers to allow re-sits for PPE/MocksWatch
Have you tried appealing? Loads of teachers in our school say a majority of people who apply, get the grades they need if they need it for a specific course they want to do. It would save you from resitting too.
Your best approach would be to speak to the relevant teacher, "I was disappointed with my performance here, what can I do to strengthen my predicted grade?".
Probably not - why should they give themselves more work just because you were unprepared? They either have to go to the trouble of finding a new exam, supervising it and then marking it - or they do the same wtith the exam you've already taken and the results won't be valid. Your mock grades don't have to be your predictions. If you put in maximum effort from now then they may increase your predicted grades as these won't go to UCAS until the Autumn.