Has this happened to anyone before??

Side note- IM FREAKING OUT

So according to the first day of my last period, it would make me 8 weeks and 3 days today. I found out like 3 weeks ago with a SUPER faint line that has gotten slowly darker of course. I just recently in the past couple days had some brown spotting and so my doc wanted me to go in for an earlier ultrasound to see what's up. She said for sure to at least see a heartbeat and we can call it good! So flash forward to the transvag ultrasound, the tech is freaking me out by saying, Uhm you aren't even measuring 5 weeks.. Maybe 4 1/2. My uterus was measuring that, as well as the TWO FREAKIN YOLK SACS she found inside!! She said she didn't see any babies just two yolk sacs. So I would literally be a month off from what I thought I was and only 4 1/2 weeks pregnant. Has anyone been THIS off before? I know it CAN happen but totally don't believe it. My first pregnancy test would of literally been a few days after I conceived then and it could be true because you have higher HCG with twins. I really can't say that I've had any symptoms until the past week my boobs got sore and bigger. My real only symptom was my missed period last month. So I could honestly just be off, or my babes just haven't grown and I have empty yolk sacs and my bleeding is the start of a miscarriage 😞

Any advice would be AMAZING for this first time anxiety wrecked momma!