When breasts are growing, they change shape and size until they're fully developed. Along the way, one breast may be bigger than the other. Of course, a girl would rather them both be the same size. If this happens to you, stay calm:

*.No. 1: You are probably the only one who has noticed. 

*.No.2: Your breasts are likely to even out as you develop. 

*.And No. 3: If you still notice a difference after your breasts have fully developed, you can use a bit of padding in one bra cup to balance things out.