Better start packing your bags, huh?
Just kidding. I would be terrified too if it were me, but honestly, I don't think you'll be in much trouble, realistically. These things happen, and in my experience the people working at the immigration authorities understand that mistakes are made, that life isn't always square etc and are more than willing to help. I wouldn't worry myself until proven otherwise. So far it sounds like a simple negligence that will demand some extra paperwork, and nothing more.