in laws think my baby is theirs

I want to start off by saying that my in-laws are generally good people. They are kind & love my husband & I & our baby. Our daughter is the first grandchild from both sides of our family so you can imagine everyone's excitement & love over her. She is truly blessed.
I don't know why, but every time my sil,fil or mil call her "my baby" it bothers me so much... it's getting to the point where it even bothers me they hold her. I'm not one to speak my mind so I keep all of this to myself. I want to stop this feeling I have towards my in laws, but how? 
I understand they love her, but I'm the one who's gone through almost 10 whole months of carrying her, nurturing her. And when I'm the one who's had sleepless nights & blow out diapers to change...
This is my child. She is your niece & your granddaughter, but not your daughter.
How do I get rid of this feeling I have towards them?