Reference a widget template
To specify a default template for the new widget, you must override the LayoutTemplatePath property in the widget’s .cs file in Visual Studio. The property must return a string that represents a reference to the full path, which represents your template, for example: SitefinityWebApp.MyFolder.MyCustomWidget.ascx.
The LayoutTemplatePath follows the naming convention <Namespace>.<ResourceFolderPath>.<TemplateName>, where you must replace path slashes inside the resource folder path with dots.