"Attendee" or "participant" by itself may cause confusion if referring to an event that has not occurred.
Get the word "register" or "registrant" in there.
"Nobody has registered to attend."
FWIW it is already Thursday here so I hope you've had both registrants and attendees. ;-)
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1