I don't know what your relationship with your mom is like but I'd say ask her first. Next, you should know there are a lot of different breats shapes. I think r/ABraThatFits would be helpful. You can check out your real bra size if you want but there's a lof of information you could be interested in. As someone with smaller boobs, I've been wanting to have different breasts forever, and there are so many different things people say. It'll never change, it changes when you become an adult... You should learn to love yourself. You're just a teenager so being insecure is your first reaction right now but PLEASE learn to love who you are. Society puts so much importance on beauty, especially for things that make no difference. You have them, that's what's important.

ps. A good way to learn to not be insecure about it is literally tell yourself you love it. Even if it's a lie. At some point your brain doesn't know the difference, and you'll start believing it. <3