Lil sister...dam it

so me n my gf were layin in bed cuddlin wen reach dwn n startd 2 rub my cock. i told her 2 stop bcuz her lil sister was aimlessly walkin around her house. she continue n got me hard. so i startd playin wit her tits. she got up,closed tha door n undressd. i did 2. she hops on top n stickz my cock inside her. she grabz my hands n places dem on her ass n tells me 2 smack it hard. about a minute into it her sister walks in n she startd screamin. i push my gf n cover her wit a blanket. her sister starts laughin n leaves. my gf was so embarress dat she gets dress (so do i) n tells me 2 leave.