I would contact your dentist immediately in the morning. It's definitely not a tumor. It is common for this to happen. I had an aunt who had the same procedure done and the same result. I'm not sure what she found out about it.
You'll be fine, it ain't gonna kill you but I HIGHLY suggest seeking out your dentist tomorrow or at least asking the front desk about that.
It's not uncommon, but I'm not sure what it could be.