HOW TO WORK MY EMPTY SIDES OF MY BUTT?

I'm a girl (15) and I'm thin I'm 5.5 1/2 I weight 105.8 and I started working out doing the 30 day squat challenge and I'm on day 29, I started to see results but after its done what can I do to help my side dents from my buttocks (I know I'm young)


But being young doesn't mean i don't worry of my figure
I will eat more to gain my calories even though my fast metabolism doesn't help me. I need to know what can I do helo my empty sides of my butt. Please.
HOW TO WORK MY EMPTY SIDES OF MY BUTT?
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