Suddenly with twins

Hi mummies...I went for transvaginal ultrasound when I'm about 5 weeks pregnant. All was OK we could hear the heartbeat. But when I went for another ultrascan at about 8 weeks, they discovered that I'm with twins. Went for another ultrasound again on week 9 and my twins are sharing a sac and placenta. I'm so worried. Is there anyone who face the same experience? Is everything OK for the babies?