I was able to get this solved by contacting the email in your original invitation email.
It only took maybe a day or two and they responded, letting me know they were able to reset the status of my forms so I could re-fulfill them and complete the invitations properly this time. As a note, they do not send the emails automatically, you register the emails and then they give you a link to send to your friends' emails directly.
Very good experience, they were flexible and responsive, spread the word that there is a fix for this.