Ivf 8 weeks measuring 6 weeks

I was wondering if anyone had any experience with a similar situation. This is our first round of ivf and we did a fresh single transfer. I had an ultrasound last week at 7 weeks and the fhr was 96, and they it was low then. I came back today and the fhr only measured 104. The doctor told me that I will most likely have a miscarriage. I am just so puzzled because I feel so pregnant, I haven’t had bleeding or strong cramping. I know the progesterone suppositories basically prevent you from miscarrying.

I’m just looking for support. I know of it’s meant to be it’ll be, i guess I’m just having a hard time accepting this right now 😔