You can't live with yourself. Go straight to Headmistress Ward and confess what happened
From Create Your Own Story
You move as fast as your legs can carry you and yank open the door to the Headmistress's office.
"I don't remember summoning you here," Ward says.
You close the door behind you. "You did not. I came here on my own. Something terrible has happened."
"What might that be?"
"Charlotte and I had a disagreement. I ended up snapping her neck between my legs." Tears are streaking down your face. "I didn't mean to kill her."
Ward smiles. "You killed her? We'll have to throw the body in the furnace tonight to dispose of it. Where is it?"
You tell her.
"I'll have my son take care of it. And if you can kill that easily, I think you'll go far in this school. I should have you take Sandra's place as head of discipline. You'd be moved to the office Sandra resided in."
That definitely wasn't the reaction you were expecting.
