No Embryo at 5 weeks and 5 days

I had my transvaginal utz at 5weeks and 5days based on utz, which I thought I was at 6 weeks and 6days based on my LMP. On this app, at 5 weeks embryo is already formed, but on my utz, it is just a yolk sac. I am a bit disappointed and sad coz I was expecting a heartbeat. Sonologist advised me to have utz again after 2 weeks to see if embryo will develop. Have you experienced this? Is it normal?