Generally when I mess something up, I put everything down and don't pick it up until I have had time to think about what I need to do to solve the problem. Knee jerk or improvised solutions have little to no place in gun building.
I have used sawdust that falls off when sanding or filing a stock with wood glue in a pinch when a small spot is needed filling. But only a very small spot. When stained and finished you really have to look hard to see it. Now on a big spot I uniformly cut out the wood and fill back with wood and glue it in place.
My worst one is drilling pins for anything. I have a jig and still manage to get them off a 1/8" or more everytime. Except the time I said screw it and drilled it by hand without any jig and it was dead on both sides... :idunno:
I guess a man just gets lucky every now and then...
"Measure, measure again, set up cut, check angle, start cut, stop, measure again, check angle, finish cut."
You forgot inletting black. The is no way to get a perfect fit without. Measuring things and marking never get it right. Measure big things, like length of pull and rough locations of parts. It is like a good trim carpenter, he does direct measurements on the wood to be cut, he does not use a measurement and then transfer it to the wood.
To install the various parts on a stock is a cut and try process using inletting black of some kind. I use prussan blue oil paint. Some use smoke from an oil lamp. There are lots of options.
I do use shavings, chips and slivers with super glue to fix any mistakes.
A top builder, showed me a couple of his first builds. Yikes!!!!! Now he builds the most beautiful rifles, that you can imagine. Some people can nail it the first try, others are not so lucky, or talented. If you happen to be the later, then you will have to suffer the consequences. I happen to be neither, and leave the building to others. I like to rework "orphan" guns, because I am a master of disaster. There are usually ways of hiding mistakes, if you think on it for a while. I guess that's why they make inlays.