You will need to be in full time education until you are 18, and two A levels plus an EPQ may not count. (I mean, there are other things you could do, but you can't just be in part time education.)
Forget some random target grade. What grades do you need to do whatever you hope to do after sixth form? If you stop doing A levels and go to college instead, those aren't gap years, it's just going to college instead and taking 3 years instead of 2.