Obviously, your sister did want the gift. I mean, who wouldn't? She's most likely mad at you for some sort of other issue. Just walk up to her and apologize to her. Tell her she was right about everything and you love her.
If she asks what exactly you're apologizing for, idk what to tell you though. You don't know and neither do I. Best advice is to just cause a distraction to avoid the question. With my sister, I will generally pee my pants in order to create a spectacle and also because fear
I don't believe in belts. There should be no ranking system for toughness.