Kinda confused (Bras)

Hey, I've been talking a lot about bras lately. So my mom got me some 34B bras without my approval or knowledge. I'm chubby for my age at 153 pounds. I made a picture of what my body shape is kind of like at the front.
So, yes, the bra was a little bit too small. But how is the bra supposed to fit on my body type? Is it supposed to just squeeze half of the thingy under my boobs? I'm new to the underwire thing, don't judge me. These are my first ones, actually, and I'm just confused. It the underwire supposed to be above it or under it or...?
Thanks for the help, I really appreciate it. This app is what I use when I'm confused about girl stuff, and since I am new, I ask a lot of questions.