Those 3 dots appear only after a few moments from sending the message and after that you can no longer recall the message or edit it. So you only have a few moments to edit or delete your message after sending it.

I agree with Nada; best thing to do now is to send another message to that person to tell them you sent them that first message accidently.

You could also mention to them that we have a horrible messaging system and these things happen a lot on italki :D

You can't delete a sent message but you can apologize to that member by explaining your unintentionally sent message.

Good luck