so messed up

I had my demo for high school this afternoon and its a perfect disaster.It feels weird that I am doing the demo class when I am not applying for any position in the school. It was the invitation of one of the top executives of the school that lead me to it. The offer goes like why not try a demo class to see if I fit either in the high school department or in the elementary department. This is because our contract with them is about to end and that they want to keep me because of the rapport I have established with most if not all of the faculty and the students. Honestly it's tempting to join them, with all the good things I could see from my present situation and I that I could do when I'm in.
I told myself, this could be my break (or continuation of the chain at some sense).I have never practiced my degree eversince and I am beginning to loose my grip on my major. And this could lead me back to it. I anticipated this day well and even promised myself that I'll do my best to keep to their expectations. I gathered materials and even brought along this ThinkPad to be able to work more efficient on the topic they will give me. And so today came, when I entered the school I began to feel sick. This could be my natural reaction to a demo class, I feel so uneasy my co-teachers observed that I look pale and that I'm my temperature is high, I just ignored it and hoped that I could still do good with my demo. But I didn't. I can't blame the class because I see that most of them have been coopeative, it's all my fault. I did not give my best to them.