PLEASE HELP! IS IT A BIG MISTAKE TO ADD AN EGG TO A BREAD RECIPE THAT DOESN'T CALL FOR IT?
There isn't any such thing as a "BIG MISTAKE" when making bread, unless you put too much salt.......
It will just add to the liquid amount. So you may need to add more flour. It will enrich the bread more, make it more tender. But you have not killed it. Who knows, you may end up with the best recipe around! :)
Here's my theory: If it's no good, it's easier to throw out a loaf of yucky-tasting bread (or feed it to the dog) than it is to throw away a pound or so of dough. And if it's good, now you know ;o)
Don't be scared--it's only bread.