--->> How do I get my PARENTS relax?

I never had a great relationship with my parents, they are very authoritarian and i am very independent; match made in hell. things got even worse as of last year, when i went away to college far away to get away from their nag. i took my new found freedom for granted and totally bombed my grades. now i am back home and literally, imprisoned. i am not allowed to visit my friends, i don't have a car, i don't have money, which makes it extremely hard to find a job and work around my parents schedule. i have a 7 o'clock curfew and i am 20 years old!! i am not allowed to hang out with my friends, i am basically on lock down. my parents and i, especially my dad, are constantly budding heads. i have bought up my grades, i am focused, but instead of seeing things i have improved, i am being criticized for anything and everything. i have no peace of mind at home and i am on the verge of running away. being home 24/7 and having to rely on them to this degree is causing even more restraint in our relationship. any advice?