S.H.
I'm not a doctor but I am a dietitian. It sounds to me like you're already doing things "right"! I hate it when doctors put unnecessary stress on families to "exercise." Your daughter is only 3 and like another poster said, she will have a growth spurt. I went from being your daughter's size to being underweight by sixth grade - don't sweat it at this point. As long as she's eating well (many of us have the opposite problem) and is active, let her be a kid. Have fun at the park, dance around the room, play hide-n-seek, go for walks through the neighborhood... my two year old son and I do these things just so that he can get that energy out!
I highly recommend you read Ellyn Satter's book "Your Child's Weight: Helping without Harming". http://www.ellynsatter.com/