Hcg levels and ultrasound sooooo confused

So I found out a little over a week ago that I am/was pregnant. Total shock, unexpected and bizarre how we even found out. Hcg levels the same day were 29.44. Two days later they were 73.97 so more than doubled. But within days basically all of my symptoms had gone away and all I was experiencing was lower back and pelvic pain/cramping. It started to feel like my period was coming any minute but super exaggerated.

I am high risk for a tubal pregnancy as I had one 5 years ago that ruptured and I lost my tube and I have several other factors that put me at high risk so per the doctors recommendations I went to the ER to get checked out. No bleeding yet.

Well, my ER visit was 5 days after my last blood draw and they said my Hcg was only 119.44. So nowhere near doubling over a 5 day time. So obviously not a viable pregnancy.

But here is where it gets confusing. They did an ultrasound and said they see a gestational sac in uterus measuring right in track with my dates. Howwwwww could they see a gestational sac with my levels only being 119.44???? That makes absolutely zero sense to me.

I am going back today to repeat the Hcg and then my obgyn wants to repeat the ultrasound Tuesday. We are all so confused though