"Come clean," of course, means you must assume they already know everything. Assume the woman who bought the ticket from you was a plant, and/or that she has already detailed all her communications with you. Assume they have a list of everyone else for whom you have ever redeemed a ticket, and that they may already have contacted these people to find out how they know you. Etc. Be completely honest, be apologetic and don't try to justify your actions, and hope that they will decide they want to keep your business.