You're doing nothing wrong.
The Top Participants in Community widget on the Your View page displays the overall top participants in Apple Support Communities - it is a global, and is not restrictable to any particular community in ASC.
To see the top participants in a specific community, go to that community's page.
You are able to select which community the widget shows the Top Participants for.
You can do that by clicking the upsidown triangle in the upper right hand corner of the widget and select Edit this widget:
Then click on Apple Support Communities under Place:
You can then start typing the name of a community and it will start to show there. Please keep in mind, you must select a sub-community, like Using iPhone in order to see the top participants in that community. You cannot set this widget to iPhone, as no discussions live in the iPhone parent community.