I am so mad at my bf's parents!!!

Pl
Okay I need opinions on this one!! I texted my boyfriends mom about a week and a half ago asking if she had to to work on Easter seeing as we usually get together. She texted back that she had to work, I responded saying "oh that's too bad l, I was hoping we could get together." She never responded. I assumed that meant we weren't getting together, right??? So I decided I'd make my boyfriend and I a nice dinner, I went out and bought everything to make. Today my boyfriend texted his mom and asked if she wanted all of us to get together on a different day, she texted back "I thought we were getting together tomorrow?" She said she doesn't work and is expecting us up there!! I'm so mad, like why did she tell me she worked and why is she JUST now telling us to come over. We have a rocky relationship anyway, I'm probably overreacting I just think it's so rude that it was never mentioned..