Hello,
1) After the demo content import you should have Popup transparent static Block (Dashboard > Static Blocks). Open the static block and find block id http://xstore.helpscoutdocs.com/article/47-static-blocks. Once you get it go to Theme Options > E-Commerce > Promo Popup and add the shortcode with your static block ID http://prntscr.com/eb6pe1
2) Check if you have this problem with our theme only. Because this is default WC widget and we don’t have such issue on our test sites.
Regards