Start by signing into Gmail with your account. Then select the gear icon in the upper-right corner, just above your email list. From this menu, select Settings.
Scroll down the General tab until you see the Undo Send section. Here, you will see an option to adjust the Send cancellation period. You can choose how long you have to be able to recall an email. You can choose for up to five, 10, 20, or 30 seconds after you sent it. If you are worried about sending the wrong email, you probably want to set the cancellation period to at least 10 seconds, just to be safe. Five seconds isn’t very long to realize you made a mistake and hit the unsend option.
When finished, scroll to the bottom of the Settings section and save your changes.