They say being lean and strong, a gung ho athletic girl is the new "sexy" compared to voluptuous curves men have obsessed on in the past. I've learned to capitalize on this since, like you, I'm lean and not big in the bosom department. If you want bigger boobs you might try implants but my preference is that you build on the assets you already have. Consult with a female trainer, one who knows her business regarding nutrition and fitness. If you train hard, you'll develop an amazing strong body that other girls will kill for when they see you in a bikini. And then, when you are properly conditioned, take up a skill to show off that bod like dancing, pole dancing, martial arts or the triathlon. You won't just be sexy you'll also be to others 'supergal'...(music playing in background) da-da-da-tah-dah!
Recently, the Greek Societies at our university had a rope climb competition as part of series of events for charity causes. My cousin entered my name on a bet and to my surprise I beat the winner of the frats...and he was a NCAA gymnast. I scurried up that 15 meter cable like a squirrel with it's tail on fire and beat him by a smidge.
So, GF, be proud of who you are.......and work it! You'll feel just as amazing as you will look!