HELP HELP IM GETTING A POOH BELLY!?

i have to go to a wedding in may, and cant go to the wedding with a pooh tummy. im a skinny girl and a poo tummy does not go well I look PREGNANT! I NEED a full excerise and food! I have a bike, 2 dogs. , for breakfast i eat at somewhere in 7am, i will eat one piece of ruit or yogurt and always gronal chewy bar. At lunch i will have fruit,sandwich/cheese/salami,manase, or pbj, water. Then eat dinner like 6 or 7 ,idk what have mom makes. I saw my mom has excersise videos. what should i do, im serious at this. is my eating good, what should i do for excerise