The plugin is actually functioning correctly, you just need to create a more specific control. Here is one example:
Instructions on creating the custom control
- Log in to your WordPress admin area and go to: Settings > Google Fonts
- Click create new font control and give your font control a name e.g Post Headings and click the Create Font Control button. (If no other custom font controls exist then it will take you straight to the add new control screen)
- Once you have created your new font control enter the following text in the Add CSS Selectors input box: h1.entry-title a (Press tab after each selector)
- Click the Save Font Control button
- Visit the customizer and you will see your new font control which will allow you to control the post headings
The instructions are the same for each font control that you would create. The only difference would be the name of the control and the css selectors that it is controlling. If you don't have any CSS knowledge any basic developer should be able to give you a hand with it. Give it a go with something else e.g. the widget titles etc and let me know how you get on.