Not an answer, but just worked with us... re: perfectionism.
As the adults, we've talked aloud about what we're thinking. So, we basically act-out the situation and verbalize it, so child will have something to see/copy (hopefully).
Eg. Draw, make a mistake. Get a little upset, like "oh no!" Then think aloud the process of accepting. Eg. "I will try again" or "I think if I practice this a few more times, I'll get better at it" or "Hmm, look at my funny drawing, ha ha, it was suppose to be a dog, but I think it looks like a bear now. I think I'll make it into a bear instead and draw a cave over here..."
After doing that a few times, I would have similar things happen, then I'll ask child "What do you think?" and let child help me accept it.
We also left things open, undone, unfinished -- at the very beginning to gently counter the demanding internal engine that wants everything "just so". But since then, we don't do that anymore.
![smile smile](/bb/images/graemlins/default/smile.gif)
Of course, none of the above works for us when child is hungry/tired/over-stimulated.
Good luck! Keep at it