Primary School Drama

There is this incident from way back when I was in primary school that still sticks in my mind. I can't sleep and somehow my mind has drifted back to this day.

So I was in second year at the time. A small group of us had been given this art task to do outside the classroom. There was this area in the hallway between the year 2 and 3 classrooms that had tables and chairs set up in it, with equipment drawers and that sort of thing nearby. We were set up at some of these tables and left unsupervised to get the work done. The teacher went back into the classroom. As soon as she left everyone got up and left the table, heading round the corner to the library area and only me and this other girl Shelly were left.
This infuriated me. I complained to Shelly that it was unfair for us to do all the work and they get to take some of the credit. Besides it was too much, we could not get the task done without more help. I wasn't going to let this happen on my watch. I said to her let's go and get them back. Shelly replied with something along the lines of forget about them. Let's just concentrate on this.
I said no, I'm going to make them come back and marched round the corner. I found the slackers seated amongst the library stacks on cushions. I told them they couldn't leave all the work to us, it wasn't fair. Miss had given the task to all of us, not just me and Shelly. They didn't care and handed me a cushion, tried to get me to sit down with them. About that point I spotted the headteacher heading this way and said as much.
At this the group leapt to their feet, throwing the cushions down and ran back to the tables. I yelled at them about throwing the cushions because this was not allowed, as I carefully put mine back on the floor before following them.
In my absence Mrs Pepper had come out to check on us, only to find Shelly sat alone working. So we were ushered back into class and I got told off along with the others.
I was absolutely incensed at this. I stood up at my desk and stubbornly refused to comply with the punishment she was dishing out, shouting at her how unfair it was. I told her I was only trying to get them to come back to the table and called Shelly out for not backing me up on that. Mrs Pepper said it was wrong of me to be mad at her when she was the only one doing any work. I continued to shout about the injustice of it all and may even have called the teacher a bitch or said I hated her (I can't remember for sure). I think she was trying to get me to stand in the corner and may have relegated me to the hallway in the end. I don't recall how it ended.
I was always the shy quiet one, so it took a hell of a lot for me to stand up in class and rave so loudly about something, with everyone looking at me. Clearly this still stings. For reference I'm now in my thirties.