Why do i feel scared to tell our parents?

Im 21 my bf is 22. Idk why im scared to tell my mom that i am pregnant. My bf and i have known eachother a little over 3 years. We been together for 3. We are both working. He went to school. He has his degree. Im about to start school. And im nervous to tell her. Maybe bc we arent married and she got married and waited to have sex and have kids after she got married but i dont have that mind set. I think completely different. But im just so happy im pregnant.