Ultrasound confusion

I went for a ultrasound at what I thought I was 8 weeks, but I got there and they said I was 6 weeks and two days and all they saw was a sac and a yolk sac. The ob didn't seem to worried about me MC he said he thinks that I'm just really early and that's what he excepted to see at 6 weeks! But at the same time I am really emtional so I wa so upset and was reading the Internet and most said they had the same thing and everything was fine but others said something horrifying can someone help me:/ he said that the next day for me to get a ultrasound is December 17th but is there any way I can get one sooner! Please comment!:/ worried 18 year old with first baby!