What should i do know? did i say the wrong thing?

Well usually, when a friend and i are in a certain class, we would sit at the back by ourselves with all our other friends in front of us( because there aren't enough sits). And today, there were 2 empty sits in front, so i decided to sit next to my other friends which i'm closer with, and i also ask that friend to come sit next to me. But she refused and said she likes to sit at the back and want all of us to move. So i told her that we have so many people, and she is only one person, why can't she just simply sit in front. She then get pissed off at me and said she will sit by herself. So i said okay and just sat down.
After a while, she called from the back saying she doesn't need to sit with me anyway, so i said "no one tells you to". Then she ask my other friend to move down one sit so she can sit next to that friend. And then that friend told her that there is an empty sit next to me and she should sit there. She then said that she hates me and that we aren't friends any more. And I'm just really shock by what she said. We aren't primary school kids, why is she making a big fuss over who's sitting with who?
She then ended up sitting next to me and telling me that she doesn't want to sit here. Then i kinda got pissed off at her and said "go back then, i really don't like people like this". And we stopped talking since then. Usually she would have lunch with us, and now she's not even talking to us.
But did i do anything wrong? should i apologise? i don't want to ....