Please, I'm Not That Mean!

I was late to class, the usual for my expectations. I’m not a bad person; I’m really very friendly. But, I’m a little stupid sometimes. My best friend Devin was with me. She wouldn’t let me arrive late alone. Well, this girl was walking behind us. She was short, with a long brown braid. That’s about all I remember about her. Well, I was walking into the school, the girl was close behind so I held the door open like a lady would do. She said “Thank you.” In my head, I either wanted to say “No problem”, or “You’re welcome.” But what had come out of my mouth was “Your problem.” This happened a few days ago and I feel so bad about it. If the girl who I said that to reads this ever, I AM SO SORRY.