Going back for another sonogram in 2 weeks, normal??

So I went for my anatomy scan yesterday and was told the sex and weight etc tge tech said everything looks good but she told me I have to go back for another one in two weeks because the baby is still small and couldnt really see the heart-baby is 19 weeks and already weighs 10oz so I doubt she couldnt "see" the heart. As i left I got the feeling that maybe she isnt telling me everything, I also started to suspect when i had my glucose test done at 12wks. I had nipt test and came neg soo im just really confused. Has anyone else been through this??