one breast is slightly larger than the other, is that normal?
Yes, this is normal. While breasts come in pairs, they are not always a perfect match. Your two breasts can develop at different rates. Sometimes this evens out, and sometimes it doesn’t — either way is normal.
If you feel self-conscious about it, you can pad one side of your bra. But even after puberty’s over, most women’s breasts, like the two sides of our faces, differ somewhat from each other.