Time Machine Problem

So I just got Leopard a couple of days ago, and hooked up my external HD to set up Time Machine. Being as OCD as I am, I clicked "Back Up Now" on the icon in my dock. It started backing up my data, but when it was about halfway through I had to do something, so I clicked the X to stop backing up data.

The Apple site said that it should be OK to do that if you need to, and if you want to resume backing up data later that's fine. But now, when my computer reaches a scheduled backup time, the backup status bar pops up and simply says "processing" forever. No progress gets made - it doesn't resume where I left off.

Is there some way that I can resume the process or am I doing something wrong? Or barring that, is there a way to simply start the backup process over? (I thought about simply deleting the backup directory on the external HD, but I get bad vibes about just doing that)