Pregnant cat small belly

Hello i have rescued cats for a few years now and i got a female about 7 weeks ago that we didnt know was pregnant. The vet said she was about 5 years old. My question is she has to at least be about 7 weeks along but her belly is pretty small i see kittens moving and can feel them as well. Does this mean she will have a small litter of maybe one or two? I know older cats have less kittens but all my other rescues have been huge by this time and have been all different sizes shes a bi color tabby kinda short and stocky vet says she may have a dwarf gene somewhere down the line and the lady we rescued her from said she had a litter with her and she was huge and had 3 kittens just wondering was all. Thanks a bunch

She sounds like she would have a small litter. Maybe one or two. Unless she gets bigger later, it differs in the cats, they could be hiding around eachother. I wouldn't worry about it!