It depends on how green and fuzzy the bread was. Was there just a spot or two and you missed it? If so, don't worry, you'll be fine. If the entire thing was green and fuzzy, you might get a belly ache.
It could make you sick, but it probably won't. Just be more careful with checking expiration dates, and start doing a visual inspection of your bread before you eat it. I've have bread go moldy on me before the expiration date, but thankfully, it's never made me sick.