I do think LynnH has good advice. I fall in the category of a perfectionist as well, but I am (slowly) learning to let go and be happy with "well done". Sometimes well done means happily done and well remembered, more so than done my way and unhappily done with some repressed anger.
I have gone to doing some invisible modeling. (I've made up this term

.) I have my ds read the entire box of plans to himself, while I do the same. Then he gets out the needed supplies, and I help get things as needed. Then, I have him do the invisible modeling. He looks at the box of plans, and step by step, shows me with his hands, kind of gesturing and pointing, what he'll be doing. For example, he might say for the watercolor painting, "I'll use this brush and dip it in water and brush back and forth over the paper like this. Then, I'll let it dry a bit, wad up a paper towel and get off any extra water. Then, I'll dip this brush in this paint, paint down to here on the paper, add this paint to the brush...," etc. This has been very helpful because he visualizes what he'll be doing, and I can see if he's off track. If he is, I'll have him look at the box's directions and help him find what he may have missed, and then I get to do the invisible gesturing.

If he is stuck on visualizing how to draw/create something specific for a project (i.e. an elephant), I'll draw a quick sketch of one on a markerboard with dry erase markers, so he can get the gist of it without me doing the work for him or giving him something to just copy. I have helped him look up pictures of this or that in his HOD books if he needs something to look at that would be helpful, but I have decided not to actually model the project for him, as both of our perfectionist tendencies kick into gear then, and the results are me trying to get him to do it my way, and him thinking he failed if he couldn't.

Anyway, this is just an idea, but I thought I'd share it as it has worked well for Wyatt and me.
In Christ,
Julie