in some cases, one boob just had more milk ducts. no matter what I do, I'm always lopsided, lol.

let the baby feed on the one that isn't and pump the other

Mine are the exact same. My daughter prefers my left side more so that side is bigger. Try getting her to latch on the side she doesn't like first, even if its only for 5-10 min. They suck better on the first breast offered and that will signal your body to produce more on that side. Do this every day and they will start to even out