I find keeping your parents in the know about what work you are doing helps. Draw up a revision timetable (I find them totally unmotivational and useless, but adults love them) which shows you have more than enough time to do all of the work you need, and each day slip into conversation the revision you've done, maybe even show your parents it and get them to test you, so that they know you're learning. Obviously, make sure you leave evenings free on the timetable, and perhaps, once you've proved the good progress you're making, ask if you can go out with your friends as you've jointly decided to take a night off from revision. That sounds lame but it's the only thing I can suggest, and it means you will be forced to keep on track with revision and your parents might actually see your point of view.
Alternatively, say you are going to study at your friend's house for something and then go out that night. Don't feel guilty. There is a massive hype over AS exams when really they aren't a big deal. Now I'm at uni I can say for a fact that even if you were given a year to revise, people would hype it up and be all 'stressed' and be revising every day and night, whether it was necessary or not. For uni exams plenty of courses only get about 2 weeks to do their revision and are still learning some of the material 3 weeks before. They manage. Don't get sucked into the hype, do what you need to do and then just relax about it. Good luck with your parents tho...