could I still be pregnant??

Do you think a baby could be missed at a 6-7 weeks pelvic abdominal ultrasound? I wasn't sure if I was pregnant or not.. If I was would have they at least been able to see the sac or something? 
It was just a pelvic ultrasound to check for cysts or anything going on in my pelvic area that could cause pain? I don't really know how ultrasounds work and I'm worried I could be pregnant but when I checked my calendar and the last time I had sex would have been 7 weeks from when I had the scan done. 
They didn't say I was pregnant in the report but I'm still stressing that I could be.