haha. Why do you masturbate naked? And why when your parents are home? I use to masturbate at night when everyone is asleep. And often jump into the shower after ejaculation so i won't have to deal with toiler paper and all that kinds of stuff.
look, it might be embarrassing but it's a normal thing to do so I would just suggest not bringing it up unless she does, and try to act like nothing happened. it's what i would do. I'm sure she understands that it's normal, so just trust in the fact that it will probably work itself out.
I hear ya, i had the same incident with my younger sis. Yeah I would suggest you tell her, and when you tell her make sure its just you and your mom and nobody else. And maybe next time you shouldn't underestimate family, because you never know when they'll barge on your door and see you jacking off frontal :)