When you schedule an email in Gmail, it's supposed to save your email to the Drafts folder until it sends. Nothing has gone wrong, but due to how we integrate with Gmail this is a restriction of the scheduled emails.
After the scheduled time, the email moves from Drafts to Sent. You can see the email has been scheduled within the web application, and it should also have the label "Tout Scheduled Email."
Alternatively, you can always schedule from the web application, and the emails won't show up in your Gmail Drafts folder.