Am I wrong

I’ve been at my job for 2 months now, the person who trained me did a good job and I’ve known her for her whole life because I’m best friends with her sister. However I wasn’t really shown how to use the app to request a day off. I had seen someone write on a sticky they needed certain days off so I assumed if you don’t use the app that’s how. My schedule is posted 3 weeks in advance, I wrote on a sticky a month ago I needed Friday off, when the schedule was posted I wasn’t on the schedule. On Monday when I went in I saw I was on for Friday, and my lead pointed out the day that schedule was printed was on Sunday meaning it has been changed. I think my manager was mad I didn’t request it off the app but I feel like it’s management issue that they didn’t explain that. The girl that trained me has only been working there a month herself.