pissed off

I thought that I did not have to go to work tomorrow because Saturdays was always my off from work but I was wrong. They want me to work tomorrow and I am not happy about it. I already had plans for tomorrow and now my plans are all messed up. I wanted to go shopping with my friend in the mall tomorrow with my children but unfortunately it will not happen. I can not say no to work too because I do not want my supervisor to get upset with me. Now I only have one day off for this week and it makes me pissed off I do not like to work more hours it keeps me away from my children.