A pending shift means that you have applied to work an event and the event operator has not responded to your request.
To check the status to see if an event operator had approved your request, try a screen refresh. In your dashboard or the event you applied to, drag from the top of the screen down. That will refresh the page you are on. If the event operator has approved your request, then you will be able to click the confirm button. The event operator has not approved your request if you still see the shift pending icon.