How do I get a flat stomach without losing weight?

I recently lost weight in an attempt to get a flat stomach but I’ve reached the point where it would be dangerous to go anything more than a pound lower (so I wanna keep that extra pound just as insurance in case I lose weight accidently one day), but my stomach is still pretty flabby for my size. I’m only 16, so it isn’t post-menopausal flab. I’m a girl, btw.