Good luck!
And don't forget to click "Submit" on the main page after you click "Save" on the app. Easy to miss...
http://ycombinator.com/apply.html
For anyone who's either considering it but thinking it's too late, or just finding out about it, go ahead and apply. They accept late apps. I only know a few YC teams (current and past) and two of them applied several days late or more. Not recommended and YMMV, of course, but can't hurt.
http://ycombinator.com/late.html