Anyone else feel too small to be carrying a baby?!

I'm almost 35 weeks. I was overweight to begin with but I didn't get very big at all during this pregnancy. This is my first. The ultrasound yesterday said baby boy was measuring on time at five pounds. I keep seeing these beautiful early babies that are around six pounds when born and I'm not understanding how my uterus is carrying something that size! I don't know where he's hiding!

This pic was 33 weeks and I haven't grown. The placenta has always been in front....could this effect it? I don't know. It's weird! I always envisioned a big baby belly but I don't know where my son is hiding in there.