I dunno if this will help much since I'm not very experienced with Wubi. I usually install Ubuntu on its own partition (the regular method). Anyway hopefully this is of some use.
If you have run the uninstall already, then it should be gone. If it's still showing the bootloader when your pc starts up, then try using
msconfig to set the default OS to windows. I
think you can remove the boot entry too, iirc.
If you have not run the uninstaller yet, I don't know why it's not showing up in the installed programs. Maybe see if CCCleaner can pick it up as an installed application.