Wow, am i a horrible person?

since i dont really know what to ask my friends of this, i usually go out on friday nights. and tommorow is my moms birthday, and she was fine with me going out since it was a reserved dinner with my family & no young kids were allowed so i thought, fine i'll go out, right? well earlier yesterday my aunt suddenly decides the kids can come, and my mom asked me and i already had my plans set, i cant just cancel on my friends! but, it is her birthday. & i'd feel sucky if i didnt be with her even though im taking her shopping this week. & i got her a card and everything and am making her breakfast. so, even though she doesnt seem to care....should i stay with her? even though i already have plans?