If you installed the plugin from within calibre, you couldn't have installed it wrong. Calibre makes it literally one-click simple
Here's a portion of my directory tree starting at the calibre plugins directory (where KoboTouchExtended.zip resides). Hopefully this helps you discover any errors.
- calibre/plugins/
- KoboTouchExtended/
- hyph.dic
- reference.kepub.epub
- KoboTouchExtended.zip
Since you're using Windows, make sure you've configured Windows to always show file extensions! Many of my problems in Windows regarding file names and locations have been solved simply by undoing Microsoft's errors in judgement.