Hey, gonna teach you something ;D
Whenever you accidentally double post or when you simply wanna delete a post you made, you click the EDIT button, then in one of the options you see Delete. Check the Delete Message box making clear you wanna delete your post, give a reason (though not necessary) and click Delete this message.
Then you won't receive an infraction for accident or you don't need to report your own message everytime it happens (believe me, it's not rare accidental double posts happen).
Well, see you around!