Eating a bit of moldy bread will not harm you so there's nothing to worry about if you happened to eat some moldy bread.
The moldy bread will taste bad so you won't want to eat much of it anyway so you wouldn't eat enough to make you really sick.
You would have to eat several pieces of the moldy bread in order for the moldy bread to make you really sick.
But just eating a piece of moldy bread will not harm you other than might make you sick to the stomach or make you throw up.
You're not gonna get harmed though if you happen to eat a piece of mold on the moldy bread or a slice of moldy bread.
I've accidentally eaten some moldy bread and It just gave me a stomach ache but other than that nothing else happened.