Yesterday one of my managers asked if she could take my shift for Saturday and I agreed too it. This morning knowing that I wouldn't have to work Saturday, made plans to go out of town with some friends. About an hour later my boss (over the manager who asked for my shift) said I need to be there Saturday because my managers request to take my shift has not been approved. I tell her I've already made plans and she's refusing to work with me on this issue. She just keeps saying I need to come in on Saturday.
Am I overreacting and should just go in or should I stand my ground? I don't want to lose my job but I would also feel bad canceling on my friends. What should I do?