You have a way to easily see a list of group or individual messages that are scheduled to go out but have not yet been sent. Go to the Messages tab and then to the Pending tab.
By clicking Pending you can see any messages that have not sent yet, but are scheduled to send. Please note this is for group or individual messages that you drafted in the Messages tab, and not for automated workflow messages that are connected to groups.
You can click on the name of the message to edit it, if needed. You can also delete that message if you no longer wish to have it sent.