Lied to my boss and feel badly

The past 3 weeks every time someone calls in or something happens, I’m the only person they call to cover, I normally always say yes if I’m available, but today a girl cut her finger (they have 3 other people and we haven’t been busy so they could handle it) and they called to ask me to cover her, but I just wanted my day off so I told her I wasn’t home right now, which isn’t true. I normally don’t lie but I know she would expect me to come in if I was home. Is it wrong of me to not go in?