Uterus measuring really big....?

Karlee • Boy Mom Survivor 💙😂

I’m 18 weeks and 1 day. Today I had a regular checkup and she said I’m measuring more than 20 weeks 😳. I’m a FTM and I thought I was big for my gestation. I’m also quite petite with not a lot of extra “fluff” so it’s very obvious. Anyone else ever experience this? I have my anatomy scan in a few days so hoping to get more insight. I know it’s insane because I had a couple first trimester ultrasounds, but could there be a very slight possibility there’s a twin that’s been hiding, or am I just carrying a linebacker? 😂 Picture below for size reference (I’m only 5ft tall)