GRA - 4th class painting

The teacher gives us a black and white photocopy of a woman (turns out she's a prostitute, but this has nothing to do with the assignment). We are to paint this in non-realistic colors. We are working in the class, so the teacher can comment as we go. And boy, do I not like that! As usual I am struggling with the paint. I so lack the right techniques to mix colors and apply them to the paper. And this is not the place where I am going to learn how to master the material...
The teacher is rude. "What are doing, she asks in a confronting way. "That's not the way to do it." I ask her to say something positive, because I desperately need some encouragement. I go home feeling so sad, so inadequate.
The good thing is I get mad. I will master this. So at home I paint and I paint. I try out all sorts of things. I spend every free moment with my paintings.