Being over 20 and still smaller than an A cup and overall undefined

It's your mind, not your body.
In my mind: My hips are too big and I look fat because of it, no matter how much I weigh. My breasts are too small. My ass is too big. My tummy isn't flat. My thighs are huge and so are my arms.
What I'm told: I'm athletic and curvy.

Not everyone likes the same type of figure but slender women are typically considered attractive. There are women out there who would kill to have a figure like yours. That's probably a horrible, shallow and fucked up thing of me to tell you but shit, you are what you are so own it.