I Miscarried (expelled The Gestational Sac And Its Content) About

I miscarried (expelled the gestational sac and its content) about a week ago and stopped bleeding 2 days ago. (I was 9 weeks pregnant at the time of miscarriage and baby stopped developing at 8 weeks.) Last night, I had un protected sexual intercourse and my partner ejaculated inside. Today, at my appointment with the OBGYN, the doctor confirmed that there wasn't any tissue left but I forgot to mention this detail. Should I be worry of a new pregnancy? Is it safe to use plan B so soon? I am 32 years old. This miscarriage was my third pregnancy.