Should young adults help care for their grandparents?

I'm a young adult who lives at home with my mother and grandmother. I moved home to live rent-free while attending graduate school to save on costs. My mom agreed before I moved in that I would not have to pay rent as long as I was able to take care of my grandmother one weekend a month. My grandmother has a caregiver that comes during the week 4-6 hours/day.

This had been going well until my mom requested a weekend in which I was unavailable due to a school related function. She told me to "figure it out", made plans anyway, and left last weekend despite my unavailability. We ended up asking the caregiver to come by for an hour so I could leave for my event.

My mom returned today and asked for another weekend this month due to a work function. I told her I couldn't because I had a test the following Monday and I already watched my grandmother this month. She also asked for the week after Thanksgiving to attend a work function but I said no because we agreed to only weekends and I have to go to school.

Am I in the wrong here? I've been holding up my end of our agreement but my mom is asking for more. I know that I'm not doing as much as my mom in terms of my grandmother's care but grad school is my first priority and takes up the majority of my time. I also work part time. I do feel bad that my mom has to compromise on work functions, but how much of the caregiving should fall to me? Should I be more accommodating?

Should young adults help care for their grandparents?
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