If you just clicked the button once then it would not have shared anything, it would have directed you to a third-party site where you could log in and confirm you wanted to share. If you then closed that site without performing any other action then you are fine and nothing got shared at all.
The share buttons are a bit dumb and do not know that you didn't actually share the link. Instead they would have simply assumed you did and presented you with the "thank you" screen.
A share is only possible if you a) click the share button, b) log in to the third-party site, and c) confirm the details of your share.
Hope that makes sense. :)