Does one have to admit to not being a virgin when preparing for a Catholic wedding? If - say as the result of a pre-cana course - the priest finds out one of the parties is not a virgin can the church then deny a marriage application? Does the priest have the liberty to ask? Does one have the liberty not to answer the question and still continue the pre-cana?
Go make a sacramental confession with a Priest other than the one conducting your Pre-Cana, and after the confession ask him. But I don't believe that the Priest is allowed to ask, but I don't believe the Church would withhold the Sacrament. Lack of virginity is not a reason for withholding the sacrament, for one can marry after the first spouse has died, and they would obviously not be a virgin.

And, just to clarify, intercourse with someone doesn't make you married to them. Unmarried, non-virgins can definitely marry in the Catholic Church.