On the beginning of the school year. ( I'm freshman) I met two girls. I sat with them a few days. One of them stopped sitting with us and the other I stayed friends with for a few months but she ended up being toxic so I stopped being her friend. The day after one of them stopped

Sitting with us, i saw her in the hall. She smiled at me but I didn't smile back. It was a couple

Months ago and I forget why. I think I was just in my own zone. We have no classes together and I barely ever see her. She probably forgot and doesn't care by now but I think she interpreted it as me being mad at her. ( just an assumption) it's been 3 months. Should I apologize? And if I do I want to do it alone because her friend group went to my elementary school and they hate me for no reason. I can't recall doing any thing mean but they always excluded me and still don't talk to me. But the very rare times I pass her in the hall she's with her friends or we just don't even make eye contact. What should I say if I should say anything at all?