[BarbieGrrrl]

some people dont grow evenly at 12 you have nothing to worry about yet you have at least 4yrs before you'd maybe want to try nbe, im sure there are loads of flat 12 year olds most probably if it really upsets you wear some silicone bra inserts i mean at your age no ones going to see them without clothes except you, and you could try massage but i know quite a few girls who never had anything until until about 18 so you should be fine.
When i was 11 i had c cups and at school everyone joked because they thought i stuffed my bra- kids will pick on anything if you let them.