John,
I know exactly how you feel, I have been there many times.
The main thing is, the only thing hurt is your pride and pocket, so shrug your shoulders, say 'Ah! well', try to think of the smiley side, and carry on.
And of course, the world hasn't come to an end, just because you have made a mistake.
As you know, I use marking out as a safety feature, from now on, I will be pop marking where the holes go as well. It just might help to make sure they stay where they are put.
John