In my early pregnancy... help!!!

Last week I found out I was pregnant and had an ultrasound done but only saw a sac 5weeks...

So they repeated it yesterday 6weeks and they think they see a yolk sac only ..... is this normal .... I’m scared... my hcg level is in the 24 thousands.... so next week I have to go for another ultrasound and I’m nervous and scared... because idk if that’s how a normal pregnancy start...!!