Christmas Eve in retail is horrible no matter where you are, or how much help there is. But yeah, you were mistreated.
Your second manager is a jerk. But don't put it that way to your actual manager. The only thing I would suggest mentioning is that the setup as it was did not allow for very good customer service. Your manager should care about that -- a lot. It may even impact their salary or bonus. So it's in their best interests to keep customers happy. And it's also in their best interests to keep their employees happy or at least around. For after the Christmas rush, there's a rush to return stuff, and as the quarter finally ends, there are likely to be sales to get rid of stuff (this is why there are Boxing Day sales, among other reasons).
And ask when you can expect your first paycheck. You have every right to know this. If it turns out it's late, ask about who you talk to, to rectify that.
A good manager isn't looking to steal your services. They want you to be paid for your labor. You can and should ask about this without further delay.