"Women's breasts are made of specialised tissue that produces milk (glandular tissue) as well as fatty tissue. The amount of fat determines the size of the breast."
Everyone breasts are different, and each and everyone is a magical sack of greatness.
In my humble opinion like eyebrows tits are 'sisters not twins' so if you feel like one's bigger than the other thats 100% normal. Big ones, little ones whatever you've got boobs are fantastic things that should make you feel beautiful babe!