So what do you do with a mistake?

Punt of course.  I started on a new painting while the other rests.  After I had laid in the wash I decided I wasn't thrilled with the composition.  Funny, because I had considered the question while I was drawing it and decided I wanted to keep it.  But, after blocking in, it looked too confusing.  My brain was screaming "Shared line issue, shared line issue", so I listened.  Perhaps you have never run into this problem...but you will.  So give it a shot, erase your guidelines and try to fill in the space with a matching wash.  We are talking about a large space here folks, not an inch or a leaf, I'm talking a foot wide.  Nope it doesn't work.  there is a tiny overlap, the color isn't perfect, etc., etc.  So you consider your options.  I considered a gouache wash, but wasn't convinced it was the look I wanted.  For a small space, I might consider a scrubber and some stippling work, but again, this was huge.  So how did I fix it?  I taped it all off, which was considerable with lots of curves, and used my Mr. Clean Magic Eraser, only slightly damp, and cleaned off the entire area.  It worked like a charm.  Some slight color adjustment and voila, back in business.  Hope you can use this tip.  Back to my brushes. 

"I seldom end up where I wanted to go, but almost always end up where I need to be."  -  Douglas Adams