Since they agreed to no Sundays when they hired you, you don’t want to set a bad precedent by then agreeing to work a lot of Sundays. I think it’s ok to work a few Sundays as a favor to a coworker who wants the day off for some special event (an out-of-town vacation, a christening, something like that). But if you say yes every time they ask you to work a Sunday, it will get harder and harder to enforce your “no Sundays” agreement. Clearly your SM likes you if she has you working 6 days this week. So, hopefully, she’s already at a point where she doesn’t want to lose you. But you need to have a conversation with her, sooner rather than later, about working Sundays. Patterns you set early in a job can be very difficult to reset if you wait too long.
I hope the weather cooperates on Saturday for you. Minor league baseball is fun.