You forgot to invite your Aunt Eloise, didn't you? And now she's doing that thing where she sweetly says, "Well, if you don't want me to be there, I understand." Don't worry. We can help you send that extra invite.
Log into your account and go to your account Sign Ups page. Choose the Created tab and click on the icon for the sign up. At the top of the sign up page there is an Admin's Toolbar with a button for Send a Message that will allow you to invite more people.
Select Invite people to a sign up, choose the sign up from the drop down and click the Select People button where you can select the option to Manually enter emails. Enter the new emails in the box and click OK at the bottom of the screen. When you are ready to send the email, click Preview & Send at the bottom of the page.
Whew. You can unpack your bags and save yourself the guilt trip from Aunt Eloise. Of course, a meme of flowers and chocolates might still be appropriate.