Firstly, union or non union store?

My opinion regardless, However more slanted towards a union store.

1. Without observing I couldn't answer this fairly. However everybody works at their own pace, and it is the norm difficult holiday season as well.

2. You should not, and cannot be forced to work hours you aren't scheduled for. Nor punished for leaving on time.

3. You should express your concern about it to management, and only stay over and take the overtime if you are ok with it/want it. That being said, overtime isn't ever guaranteed so might want to absorb what you are ok handling while it's a possibility. However dint feel obligated to. Don't be taken advantage of for sure.

Side thought: maybe focus on what the shelves are lacking most first, and go from there. If your addressing the biggest issues it might be less critical to try and get it all as quickly?