Don't let your teacher or classmates hold you down, give it a shot!
To adress some issues:
- GCSE's don't matter that much. Yours won't count against you, they're good enough for them to stop caring about them.
- The location and type of your school is irrelevant. Actually, it might even count for you instead of against, they compare your grades to what is usual at your school, so if your school usually performs badly, your grades are even more impressive.
- They won't particularly like the B in AS Maths, so maybe be able to explain them why if they'd ask in the interview, and be sure you have an A prediction for A2, or A* if possible.
- Drop the B A-level, not worth the time and effort, they only care about A's.
- In some schools, you can influence your teachers predictions by just talking to them and asking them to predict you a high grade. If that's possible for you, try getting A* predictions next year, wouldn't hurt.
- EC's don't matter that much. If you'd have them, they were relevant and you could explain what you learned from them, sure, it's always nice. But it'll never be the thing the decision is based on. Don't stress about work experience, it's far less relevant for PPE.
- In PPE, the TSA test everyone has to sit early november is very very important. They use it to cut off a large number of people pre-interview and I'm 99% sure my very high score made up for my pathetic excuse of an interview. Make all the practice tests you can find and maybe read a book on critical thinking.
- Go crazy obsessive over your PS. Start writing it right after AS-exams (before that, you'll need to spend all your time studying) and just improve it every week. You'll keep getting new ideas and small changes that make it better. Then when the school year starts again, ask teachers, parents and people here on TSR to proof-read for you and give you tips.
In conclusion: make sure you do everything you need for your application the best you can and just go for it. Trying never hurts.