How to get a flatter stomach?

Hi, i am a 15 year old girl and im looking to get a flatter stomach. Im short ( 5 foot) 100 lbs, and i am fairly skinny. The only problem i have with my body is my stomach. i know im not fat by any means but i would like to get rid of the little extra fat at the bottom of my abdominals. I would like to have my flat stomach by the start of my high school years that is coming up in September. any ideas?

ps. i don’t want to go on any "diets" or any thing because of my age and knowing that im not big enough to actually need to go on one…just eating a bit healthier maybe?