We have a book called "Beautiful Oops", that DD loved (and still loves at 4.3).
She went through a strong perfectionist stint around 2.8 and we struggled with explaining that coloring in the lines and backwards S's weren't a big deal and could be "fixed". After reading the book a few times she started to creatively think about how to make something from her errors and not get so upset about them.

We also started addressing all of our errors with laughter and making fun of ourselves for them (that is not easy for 2 perfectionists) and she started doing the same. At this point we ALL ask each other how we could fix things that aren't 100% what we wanted, and come up with new reasons they are the way they are!

We have found all of our creative problem solving skills have been on the rise & the annoying quest for constant perfection has started to dwindle, replaced by "that's OK" and "how do you think we can take care of this"?