Draft email disappeared after hitting "Save Draft" button

After typing a rather lengthy email, I had to stop working on it before I could proofread. I hit the cancel button and then "Save Draft." When I was brought back to the inbox, I immediately hit the mailboxes button. Later in the day, I went to finish/send the email but it wasn't in my drafts box. I searched "All mail" both on the phone and on the Gmail website without success. I've used the save draft function many times before without any issues. My hunch is that because I clicked back to mailboxes so quick, the phone wasn't able to sync the message with Gmail. But since I'm not a programmer, I could be wrong. If anyone could enlighten me how the save draft function works with Gmail I would appreciate it.