Had my first sono yesterday.. :(

I'm kinda freaking out but my so is trying to help me stay calm. I had an mc in December. Yesterday we went in for our first sono. And from my missed af I should be 7 weeks today. There wasn't a visible baby. Only the yolk sack. I don't know if it's possible that I ovulated later because I only had one period in between So my dates are off? I'm kinda scared of having another mc. I know I did buy the test you are supposed to find out before you missed a period but it didn't show positive until several days after I missed it.. Idk I am just nervous.  Has anyone else had a similar experience? I just want to have a positive attitude while we wait for our sono next week.