Pizzed off (non mommy related)

I hope you don't mind me posting something non mom releated. At work we have to work weekends - 1 a month. And we each have to choose a holiday to work. So I am also working President's Day which means I'll probably work Saturday and Monday. Fine no problemo. So the co-worker that prints out the sheet we sign up for weekends wrote on top that I only have to work 1 other weekend day (because I'm doing Prez's day weekend). OK no problem.

Now 3 days prior, I was (joking I thought?) and said "I'll take anyone's days if they don't want them". I was half joking. So this one lady that never likes working any of her days said "you can have mine". But I didn't know she was 100% serious. So when it came time for me to put down my weekends I wanted, when it said on the sheet I only needed to pick one more I figured OK that other lady doesn't want to give up her weekends afterall. So then it turned out that there were some weekends not chosen at all (the list gets passed around by seniority, I'm 3rd from the bottom so of course there's extra days after I choose). So then my manager is saying something like I have to take extra days. I said "no one told me this" and I dunno she kinda got huffy like as if I said I would do it then changed my mind. I didn't change my freakin' mind, I thought the person that said she'd give up her weekend changed HER mind since it said I only needed to choose one more weekend from the lot.

So now I'm the bad person and I swear I'm never again telling anyone I'll take more weekends ever again because then when it comes time to do the schedule, no one tells me that still stands and I end up looking like the a-hole that goes back on her word.