I'm going to miss my friend's two hour 21st birthday party on new years eve
Oh, no. Why are you missing the party?
I don't want to go there and I know my friend doesn't want me to be there.
Still, it is a 21st birthday! You should not miss the celebration, especially if they are good friends. It is your duty to be there to support her.
If I go there, I know that I will end up causing trouble and I will have to explain myself. I have better things to do.
If you were invited then you should go. Clearly they want you there if you were invited. Give your friendship more credit instead of assuming you're unwanted.