Was I wrong in responding this way to my boss when she asked me if I could work?

Maybe I’m over thinking this
But I got a text from my boss/manager whoever she is to me I don’t know that said “can you work tonight” and I said I can’t because well… I can’t. I’m going to a family members house. But I didn’t give any reason I just said “No, I can’t. I’m sorry”
Was that not how I should’ve responded? Because looking back I’m thinking that maybe it wasn’t a question but a request…