Is it legal for your employer to mark you down absent if you showed up o work an hour and 40mins late but still worked the rest of your shift?

My schedule was changed twice and I was unaware because it's never happened before and as soon as the schedule is posted I mark down my days off on my time sheet. I thought I was off because that's what I was aware of and that's what I had written on my time sheet but my boss called me that day and asked if I was coming in, I said, "no, I'm off today" but she said I was scheduled to work long story short...i told her I would be there as quick as possible but I live almost an hour away and I had just woke up and I still had to get ready but I went to work and I stayed my whole shift and I got written up for it and suspended because they said it's considered an absence???