I guess I'm gonna be that guy.
I don't think it's acceptable at all. It wasn't a mistake. It was outright planned theft. You took their box and changed it hoping no one would notice. You got caught and now are coming forward before someone else says something first. That isn't owning up because of guilt or shame in my book. There was no guilt or shame when you gladly accepted the Top 5 win. No guilt or shame preventing you from creating multiple boxes since INCLUDING another Peter Pan's Flight for the Disneyland Project. That's just thinking you got away with it and staying quiet.
As a writer in my spare time, I can never look past plagiarism of any kind. I think that "win" should be removed from the Toy Box Artist Leaderboard on here, or at the very least asterisked like some sports stats.