I gave away one of my shifts at work and I refuse to take it back.
Why do you not want to take a shift back?
My manager is a bitch. I hate it when she gives attitude to me at the supermarket. I don't want to do what she says.
You gave that shift away, so you don't have to take it back. You already made the decision to do that.
But I'm the one who decided not the manager and I think she is the one who should listen to me.
That isn't how it works, your manager will never be the one who has to listen to you. With that said, though, you shouldn't and probably won't be expected to have to take something back that you already gave away. You should be fine and you're worrying about nothing!