Am I a bad sister??

I'm supposed to babysit for my sister tomorrow, and i only said yes but only if she pays me and then she sent back a reply saying dot dot dot ok, so now I feel bad for asking that even tho I never ask for it in the past but she would pay me anyway in past. But if I try to explain it to her I feel like she won't believe me and think that am just making excuses but I'm not, I just don't want to be a bad sister, fuck! Why is life so hard....