Yea that sounds awful. You can just decline, though it sounds like you might be non-confrontational, and might be the reason you started doing all this in the first place, and probably due to you wanting to do things the right way.

When I see an imbalance in tasks I say, “maybe not today, I’ve being doing this this and this during these last shifts, but I can help with so and so if you’d like”

They may be a bit surprised, but usually won’t fight it if there’s truth to it.

I would also maybe see if you can chat with your store manager via email/ chat or phone if you felt awkward to do so in person, though that is the best way. But I would not continue on like this if it is affecting you negatively, the job isn’t worth that, and you can just as easily find another job with the work ethic you describe. If your schedule allows you the option to change schedules (like requesting not to be put on closing shifts, or shifts with this closing sm), and then from there explain why. But if you’re not willing to stand up for yourself, no one else will. Chances are that new shift is overwhelmed , and just isn’t as organized. If you are willing to take over being a shift, that’s something you can discuss too, especially if you’re already doing the work. But again, you need to speak up, or nothing will change, and if you aren’t able to do that, I would just change shifts, locations or job in general. Go somewhere that’ll make you happy, or at least stress-free.