What to do when meeting my boyfriends entire family when his sisters dislike me?

Me and my boyfriend are pretty serious and he wants to bring me to this huge family party on the 4th of July but here is the problem, two of his four sisters hate me. I had said something they took offense just a few days back and even though it wasn't meant the way they took it, they didn't care about my explanation or my apology. (I had said I didn't want to spend all day with his family because felt weird around them meaning that I felt nervous and was too worried about their approval to have fun) Well, now I don't know what to do if I am confronted by them or how I am supposed to act while being around them. I am already really nervous about meeting his parents for the first time and this is adding on to my anxious feelings about this day. Any advice would be great!