Can’t cover a shift

I work as a casual sales assistant in retail and while I was working (on a Friday) was asked if I could work a day on the weekend, it was very busy so I said I could without thinking (silly of me). When I got home I remembered I had important plans with family so I texted the same night apologising that I could not make the shift but I got no reply. Would I need to show up or can I not go? (I know they would have seen the text, managers check texts constantly)

usa jobs
usa jobs resume
usa hotel jobs
usajobs
usa jobs federal government
usa job in ksa
usa jobs
usa jobs login
usa jobs gov
usajobs.gov
www.usajobs.gov
usajobs.com
usajobs
usajobs.gov official