4wk3d ultrasound

I went for a blood test and ultrasound today. I am about 4w3d(they didn't tell me that, it's my calculations) Blood test came back fine, my numbers are all good. On the ultrasound they were able to see the gestational sac, but no yolk sac or anything else, which they said they didn't even know if they'd be able to see anything at all today so that made me happy. But then they called and said to come back in a few days to see if they can see the yolk sac yet and of course that made me nervous!!! Anyone else have a similar experience? Just a nervous wreck. This is our first baby and been trying for 8 months.