How can I make your form pop up when someone clicks on a graphic on my site in Muse?

You can insert our form in the pop-up by using the iFrame embed method. Please take a look at our guide on how to get the iFrame embed code. You should then be able to insert the form in the popup as a template. 

I didn't have any experience with Adobe Muse but if pop-up plugin supports adding custom HTML templates you should be able to use the method I have suggested. 

Please let us know if you need any assistance.