size of belly correlate with size of baby?

So I don't think I'm super huge, just average I guess for how far I am. Sometimes I look really small compared to many bumps I've seen. 
But I got a 4d ultrasound and although she only saw his face and hands she kept saying he was going to be a big baby. 😑 which was making me angry. I didn't like her calling him big and " fluffy" I didn't think he looked big , I mean a lot of babies in 4ds looks super squishy lol there floating in water of course they look chubby cheeked. But she even made a comment saying I look small but he sure isn't. .... 
I was just like well why wouldn't I look big if I had a big baby? I measure smaller then how far I am.  
Idk if she understand how rude that is to say to a mother though. Like don't you talk about my baby unless your calling him perfect and healthy. 😑🔪
The pictures suck so it's hard to even see him. 
I was overall not happy about this ultrasound. The price was insane and we got no photos that are clear. A disc of 55 pictures that all look the same. But does anyone think he looks like a "big baby" or just normal ? I'm 31 weeks