I get that all the time, from my mom even! After I got a 4D ultrasound pic she has quieted down about it being twins, but she still comments on how huge I am. My sister also got really big with her pregnancy, she was definitely bigger than me but for some reason my mom must not remember clearly because she keeps saying I'm bigger. Which is so not true, even my sister agrees. At 24 weeks my mom thought I wouldn't fit in maternity clothes anymore. My stomach is big, but it's not that big! And now I'm 31 weeks and guess what mom, I can still wear some of my regular tops!
At my shower, some people would say I looked so big then the next person to come up to me would say I was still so tiny. And some people say I have gained only in my belly, then how come I can't cram my sausage thighs into my old jeans and I've had to go two sizes up? Maybe my belly is hiding my legs if someone is facing me and standing up? :)