you didn't let anyone down just like LastBreath2 said. Don't worry you may have messed up now but everyone does. You'll have another shot at it. Don't let life's little mistakes bring you down =D
You're human, aren't you? LastBreath2 is right, you didn't let them down.
=) The people you dance with know you don't often make mistakes, you know you don't often make mistakes. Occasionally poo happens, but that doesn't mean that you're not a fantastic dancer and it doesn't mean you let your entire group down. I'm sure if one of them made a couple of mistakes in the dance you wouldn't think they'd let you down.
It sucks because you've practiced so much and didn't get a platinum (I've no idea what that is btw..) but hell, what's done is done. As long as it doesn't knock your confidence enough to stop you dancing then ultimately it doesn't matter now.