Your code worked for me; The widget appears in the admin area under Appearance > Widgets and the widget does show output on the front end.
Your widget() method is missing the output for $args['before_widget']. echo $args['before_widget']; should be added above <section id="box" class="box1">.
This would not cause the issue reported, where the widget does not appear in the admin area, but it will cause problems with the HTML output on the front end.
