Dark-Corner-Girl: Touching

Today one of my friends sat behind me and just randomly started to touch my back. I hurt her ... Not like I wanted to but ... I don´t know. I just really don´t like people touching me. I don´t get it why people do that. Yes, I hug people, I like doing that but other things like just a light touch... I don´t get it.
I didn´t want to hurt her but I did. I pushed her hand down and her hand hit the chair. She was pretty mad at me. Half of me was like "I am so sorry!" and the other half was like "Don´t touch me!" and I say the last thing out loud. I still feel bad of course. She showed me her little red spot what she sayd really hurt. After a little while she was laughing again. I smiled and laughed slightly too - cuz it is really easy for me to do. But in the inside I felt a not hurting pain. Which was even more killing. Why am I that bad of a person? Why didn´t I say that I am sorry?
Why was I a bad person and sayd "Don´t touch me!"?
She IS my friend after all...