I catch my horny step sister watching porn and ends up fucking her so she can have her orgasm

I enter my chubby sister's room and surprise her watching porn and masturbating, I offer her if she wants to fuck so she cums and she says yes. Then we fuck in several positions doggy style, missionary, reverse cowgirl and she ends up having an orgasm in missionary position while imagining that the guy in the porn video is fucking her.