You may set a limit on the number of Spots each Participant is allowed to sign up for in the Details tab of your SignUp's Organizer view (towards the bottom of the page). This option is available with any of our Premium plans (starting at $9.99 per month).
If you have also selected the option allowing Participants to Sign Up Others (friends, family or team members), then only the designated number of Spots per Participant being signed up will be allowed.
If you have already launched your SignUp, please go to the Participants tab of your SignUp's Organizer view and quickly review the number of assignments to see if anyone is already signed up for more Spots than you intend. If so, please manually make adjustments by deleting their extra assignments from the Participants or the Spots tabs.
For a tour of all your Organizer options including navigating to the Details, Participants or Spots tabs, please watch the quick video in this help article: Managing your SignUps