To at least find the silver lining here; I can polish off my plans a bit, and I can polish off the material that I've given the players so far too; make it a little bit more coherent and organized, and give them a bit more of it while I'm at it. And heck; maybe I can bust my hump to get my big poster map finished and painted before then so I can show them where they are while I'm at it. I can actually stat out some of my villains, make better plans for the various encounters, maybe photocopy the pages from the monster books that I need (so I don't have to actually take the books with me--even if it's just coming downstairs at my own house) and otherwise be a bit better prepared than I am now. It also gives me the opportunity to print off some images that will make the session more evocative.
All in all, I'm going to force myself to see this as a positive and come up with an even better session than I otherwise would have when we get together next!