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I've already made other plans for monday. It wasn't a backup for in case you forgot, it was just for until you could confirm if you could make sunday (which you could)
You mentioned Monday as a backup time which was contingent on your confirmation for Sunday. Since you confirmed Sunday I made other plans for Monday because the backup was no longer needed, as you were able to play on Sunday.
Again I'm sorry but scheduling with a 17 hour time difference is really awkward and I messed up and forgot we were supposed to play at the time. Again, we had today as a backup and it was agreed by both of us.