Is it wrong of me to not want to be watching my nephew all the time?

My sister always wants me teaching my nephew alphabets, numbers, or doing stuff for her, which I do most the time but I dont want to be doing that all the time. I want to do my own things as well for me and she expects me to stop what I'm doing and if I don't then she gives me attitude or acts passive aggressive its so annoying or she says I'm selfish or something

Is it wrong of me to not want to be watching my nephew all the time?
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