Who is right, my mom or me?

Hello, I am 20 years old. I live with my parents like most people my age. I have a couple of friends and I don't really go out. I'm a full time student and I have good grades, I'm not irresponsible. I've gone out a few times and stayed out late a three or four times but really spread apart like during 2 years. I live in the mojave desert and to do anything fun, you have to drive down the hill because it seriously sucks here and it's really boring. One of my friends like to take us down the hill sometimes but I always say no because my mom doesn't want me to. I mostly stay here locally when I want to hang out with friends. Last night I came home late because my friends and I wanted to go to Santa Monica beach, so we went there and came back pretty late. I told my mom I'd try to be home at 1 am but then I called her to tell her I'd get home later and to fall asleep and not worry. Anyway she never listens and she stayed awake all night waiting for me just to open the door and tell me she can't sleep because of me... I came home at 3 in the morning and since the hour changed forward, she says I really came home at 4 o' clock...Anyway she's not healthy and she says every time I leave the house and come home late I make her really sick and that I'm gonna kill her and my dad gets really mad at me. I'm so happy when I'm out with my friends but then it just ruins it when I get home because I can never feel good about being happy and going out with friends.... How can she put that much guilt on me?? Am I really responsible for this? My friends tell me it's time I cut the chord and they control me too much. Apart from this my sister was a little crazy at my age and I've always been the responsible studious one. She ALWAYS tells me she would expect this from her and not from me, basically making me pay for her mistakes and that she already went through enough with my sister. I feel like they are overprotecting me because of things my sister did. I hate most of all when my mom says I make her sick because it just makes me want to never go out. They never even let me spend the night at a friend's house. I had to beg and ration with them on new years that I'd be safer at my friend's house than on the road and I'd have a higher chance of dieing trying to drive home because of all the drunk drivers. The excuse is always what "could have happened" and I always say, "Well it didn't happen! I came home didn't I? I'm okay, aren't I? " and it's just always the same with her saying I make her sick and don't let her sleep. What would you do in my situation?