4/5 week ultrasound saw nothing?

Is this normal? The dr only saw the gestational sac which was a small little circle. My period indicated to me about 6 weeks, however they measured at less than 5 weeks. She didn’t see anything and had me do blood work Friday to check HCG levels and I will be going back today to see if they doubled. I won’t get a call until tomorrow. She thinks I could’ve ovulated late, but told me to be prepared for anything 😭😭😭 she said she’ll call me work the results and to tell me when they’ll need to see me again!