Unfortunately facebook doesn't have this option available, luckily, there is a work around, and this is what you have to do to cancel those 'accidental' add-ups:
- Log on to your account at www.facebook.com
- Go to Settings at the top of your homepage.
- Click on Privacy Settings.
- Click on Manage under the Privacy tab.
- At the bottom, find the Block People option.
- Type in the name of the person that you do not want to be friends with (see "how to search" below).
- Click "Block". The person is now blocked from your account.
- Now, go back and type their name in the box again to unblock them.
- The pending friend request will disappear from their profile page and they will never know that you temporarily "blocked" them.
You can opt to keep the person blocked from your account permanently by omitting the Unblock step. This way they will have no access to your profile and no option to ever send you a friend request.
--> In the search box, type in the name of the person you inadvertently Friend Requested, hit search.
--> For a pending request, it should read Awaiting Friend Confirmation under their name (if their profile page is private, it will read Friend Requested next to their name on the main search page).