It does seem like you are not setting your own course but letting them rule what you do/don't do. You went back to the car when you couldn't get into the club and then decided to go do something else but came back for your sister. When you were in line and wanted to do something else (besides stand in line an hour and a half to not get in!) you should have said, "see ya, I'm going such and such a place", gotten the parking ticket from your sister (why did she have it if you were driving?) and gone and done whatever. You make a decision but then change it back based on what they think when they aren't thinking of you.

Whether your friend/roommate believes you told your sister you were going home or not, you know you did (and your sister knows you did) so that's that. You say, "You're welcome!" when she texts you a snippy "thanks for not telling your sister and making me go pick her up. . ." and maybe, "When are you all going to get here?"

I would try to make a few more friends, join an interesting club or something at school. I understand about only knowing a few people and being shy; I did the same had the same 2 friends only from high school and the one roomed off campus with other people, didn't ask me, etc. I wish I had tried harder to live my own life but I kept to myself also. Think longer term; when school is over and you are working or dating, etc., those two aren't going to be there in the same way, whether you or they want to be. I would try to get a broader base so the transitions are easier? If you have your "own" thing, a club or some interest they are not part of, that can teach you how to adjust to your own life circumstances more comfortably as well as maybe furnish you new contacts in an area where you are more compatible. If you love to read rather than go clubbing, there's nothing wrong with that/you, but you might be more comfortable and have less difficulties if you are in a study group or library setting instead of sitting in the car by yourself. Yes, you probably need to "get out" more but probably not with these two, on their turf?