Feeling worried 😞

I have had a previous miscarriage and then had our rainbow baby who is almost 11months now. I found out I was pregnant again about 2 weeks ago and although I was shocked I'm really happy. We decided to book an early pregnancy reassurance scan as over Xmas I had a girls night out and overall just to make sure everything was ok. We went to the scan this morning and all they could see was an empty gestational sac. They've asked us to come back in two weeks incase I'm not as far along as I thought. Im trying not to freak out but I genuinely expected to see a yolk sac so I've now got it into my head we are going to lose another one 😞 I'm so grateful for the baby we have but I was hopeful we were having another one x