GMail has a feature called "Undo Send" which will give you a period of time after you click send to "bring it back." To enable this, please follow these steps:

Click on the gear icon in the top right of your browser window when logged into your GMail account and choose Settings.

In the screen that comes up, look for and check mark Enable Undo Send. You can set the amount of time from 5 seconds to a max of 30 seconds.

Now when you send an email, you will see this at the top of the screen for the amount of time you set in the steps above..