The 39-year-old actress - who gave birth to Sadie Grace, her first child with her 41-year-old fiance Martyn LeNoble, on January 27 - is determined to do her best in all aspects of parenthood, but admits she has moments where she doubts her ability.
She said: "I want to be the ultimate burper and diaper-changer, I want to be the ultimate at all of it.
"Sometimes I stand there going, `I`m not doing any of this right!` And then I get this big man belch out of her and I go, `Ah, we accomplished this together.` "
Christina battled breast cancer in 2008 and she says it is only now she is a mother she feels completely "healed".
She explained to People: "I`ve had to talk about that word [cancer] more than I`ve ever had to talk about a word in my life. After a while you`re like, `There`s got to be something else to me.`
"Yeah, now I`m a mom. She`s healed me in so many ways. She`s just made my life so much better. She`s opened my whole soul.
"I felt my heart literally open up for the first time and like wrap itself around her. It was profound. And I`m more in love with her every minute of the day."