2 ultrasounds??

Has anyone ever had to do an ultrasound twice in a two week or less span and everything was okay? I'm measuring earlier than I thought and had an ultrasound yesterday when I was 5w 6d, not 6w 4d as originally expected. Since I was before 6 weeks, they want me to come back next Thursday, when I'll be 7w 2d. They didn't seem concerned - we saw the baby and the yolk sac and the heart flutter almost immediately...105 bpm which she said was on track for how I'm measuring. Is this okay? I know they don't do ultrasounds all the time but should I be concerned they want to do another one so soon?