Why compare your baby with other people children? Do you have any idea what baggage some people carry about, they might be unhappy and drop irritating hints about your baby's weight so you can be unhappy.
Why not concentrate on being happy and taking good care of your child because babyhood goes really fast and you don't want to miss that milestone by worrying.
At least your baby feeds well, some babies dint feed well and they still put in weight, just continue with what ure doing and you can let your baby have a nap during the day.
Speak positive things to your child by prophesying the good things you want and see in her life rather than comparing other people's babies to yours.