Not at all! I had a u/s at 28 weeks this time and looked up expected fetal size. Our guy was smaller - near 2 pounds - and fell in the "expected range".
As for your size, it depends on your body structure, your fitness level (muscle tone), baby position, etc. Remember too that we don't typically know others are pregnant until they are 12+ weeks... I think that tneds to make us have skewed views of how "pregnant" we should look early on.
don't forget that baby puts on a lot of weight at the end of your pregnancy. and the size of your bump isn't really all that important. i met one woman who said she was due in two weeks and she looked like she was 4 months! i mean, i wouldn't have known she was pregnant if she hadn't pointed it out. every pregnancy is different. plus, in a few weeks that might all change. i say appreciate the smaller tummy while you can. as long as your doctor says everything is fine and you are feeling kicks, i wouldn't worry about the size of your belly.
Everyone is diff in pregnancy when it comes to showing, but an average baby around 29 wks is 2.5 pounds so your baby seems fine.