I'm surprised they didn't secure the down-payment from you before you left the dealership. That's their fault. However, in order to get financing, especially in this weak economy, and for a motorcycle no less, you HAVE to make a down-payment. It may not have been discussed because it was probably assumed you knew that a down-payment was necessary. I'm surprised they didn't ask you how much you were going to put down though, that's weird.
I would pay it as soon as possible to avoid a late fee, or worse. If you can't afford the down-payment, you may have to get the dealership to refinance the entire amount, which they would likely do, at a much higher interest rate.
Sorry for the long post, the banker in me came out. Oh, and I wouldn't scan the contract and place it on a public forum, just for your identity protection. Good luck getting it resolved and let us know how it works out!
Not all who wander are lost.