Registering a plugin as a widget

I’ve got a fairly popular plugin (fundraising-thermometer-plugin-for-wordpress) that I’m trying to get running as a widget but the code is throwing errors when I add the code:

class OurProgress extends WP_Widget {
	function OurProgress() {
		$widget_ops = array('classname' => 'our_progress', 'description' => 'Our Progress' );
		$this->WP_Widget('our_progress', 'Our Progress', $widget_ops);
	}

	function widget($args, $instance) {
		extract($args, EXTR_SKIP);
		 echo show_ourprogress_graphic();}

	function update($new_instance, $old_instance) {}
	function form($instance) {}
}
register_widget('OurProgress');

If I add this code to the function file, it works perfectly but not in a plugin file.

Can anybody help? I’d love to add the functionality to the plugin but widgets are outside my area of comfort.

thanks