Pissed off -am I wrong?

I've been so moody and irritated lately. Everything bugs me. I'm annoyed at the fact that my mom offered my grandpa MY car for the weekend when I already told her I have plans. I'm supposed to help my girl friend move tomorrow and then spend the night at my boyfriends. Now this ruins my entire weekend. I can't even go to my boyfriends tonight because the cars is needed tomorrow morning. She offered me her car tomorrow night to go to my boyfriends but said I need to be home by 9am so she can go out. Like no, I fully said I had plans this weekend, and she didn't even ASK for my car she offered it up anyways. I'm beyond pissed off and just needed to rant. Is it wrong for me to be pissed off?