Call me "step-mom"

For a few seconds after she has finished cuming, Millie just lays there, then she opens her eyes, and feigns being shocked at the sight of cum on her feet, and says:

"You dirty little boy, look at the mess you have made."

I blink a few times, not sure what to say, but then I say:

"I am sorry Millie."

Millie leans forwards, and slaps me across the face, and says in a strict tone:

"Do not call me by my first name like we are equals!"

I rub my cheek with my hand, I can feel it growing red, and say:

"What should I call you then?"

Millie just looks at me and says:

"If you were older you would be allowed to call me 'mistress', but as you are just a dirty little boy you will refer to me as 'step-mom'. Do you understand?"

"Yes." I reply, and then, seeing anger flicker in her eyes on hearing this, I say:

"I mean, yes step-mom."

Millie looks at me with eyes showing she is pleased, and says:

"That's a good boy, now go get tissues and clean up the mess you made on my feet."