I was like you in my first miscarriage... As early as 6 weeks, some could detect baby's heartbeat already. But to have a more assurance, go seek 2nd opinion, that does a vaginal ultrasound.
Have a chat with your gynae for medication to expel it naturally or schedule D&C.. I went to 2 gynaes coz I couldn't believe, both gynaes did not advise D&C..
Big hugs, take some time to cry and get through the pain.. Soon your rainbow baby would come by..