Hcg levels.. ultrasound next week.. nervous

So per my LMP I’m 7w3d today but they checked my hcg levels around 6 weeks & the first time it was 138 & 2-3 days later 667… so they said it’s good that it more than doubled & are thinking I may just be a little further behind. Seem a little low to me. I’m just so nervous! My first ultrasound is next Mon Jun 7 & it seems so far away! With a past miscarriage I’m just praying so hard all will be ok & a little baby will be there. Just needing to vent my feelings.. maybe someone has had similar numbers or a similar story ❤️