Told my boss last week was my last as I was going back to school and asked if I could let her know if/when I could work going forward. Now her being short staffed is my problem

For content I work as a server assistant in a restaurant. When I was hired I told her I would be going back to school and let her know my last week. She said “Okay!” and that whenever I could work would be helpful because she didn’t want to lose me. She scheduled me past my availability and I reached out immediately. But now her forgetfulness is my problem.