If you make a typo or regret sending a message, you can undo the action by enabling the "Undo send" lab. This lab will give you the option to take back a message you just sent.

To enable the lab:

  1. Click the  gear in the top right.
  2. Select Settings.
  3. Click the Labs tab.
  4. Find the "Undo Send" lab and select the Enable radio button.
  5. Click Save Changes at the bottom of the page.

Select the amount of time you have to undo sending a message by clicking the gear icon , and finding the "Undo Send:" section in the General tab of your Settings.

REF: https://support.google.com/mail/answer/1284885?hl=en