Baby or no baby?

Six weeks today and went in to an ultrasound because of light brown spotting for about an hour.  She did the ultrasound and said she thinks she sees the baby but she isn't sure because it might be laying weird. She said the sac looks beautiful it was just hard to see the baby. She said the little dot in the sac might be the baby but I have to go back next week to make sure. When she measured the little dot it was measuring six weeks. Should I be worried or does it look promising? I've seen so many people see a heartbeat at this stage and I'm so upset that I didn't.