OK, after looking at your source, it seems you are trying to place the ninja shortcode as the target. This is not how the plugin works.
First you need to place the ninja shortcode on your page. Can you see the form on the page now? good. This form will have an ID or a CLASS assigned. you use THAT id or class at your target. It is not an issue with the plugin, you simply need to read the documentation.
1. Get the form displaying in your page correctly.
2. add the print button using the form’s ID or Class as it’s target.
Good luck!