What's the Name of That Book??? discussion

Girl lives in a world where superheroes and villains exist. Comes from a famous superhero family. Has an older brother. One day she finds out that she has a twin which is really bad. In this world twins are born either goof or evil. No on knows which one she is. And if she turns out to be a villain she be killed. Hero’s live in their own city?

She debates over if she’s good or evil. Friends start to out her. I think she problems with her powers.
Then she finds out her twin is still alive. She was raised with villains. People with powers are born good or bad. Villains have a genetic property that makes them evil(?).

She runs away from something I don’t remember why but goes to her friends(?) lab in the ocean. He’s kinda rich and labeled a nerd because he’s a scientist. Tries to learn about the evil gene.

This lady who makes superhero uniforms makes hers black so she could she it doesn’t matter. That doesn’t work.
There’s a break in, but it was actually a trap that was designed to catch villains. She didn’t know and she got in trouble.

Read in 2015-16. The cover was like a girl's outline with a kinda pastel color, I think.

City of Legends by Cheyanne Young?

Yes! City of Legends is the book. Thanks Ayshe!