Need help with contractor issue.?

hired a contractor to redo two bedrooms. one room had to have drywall installed and crown moldings moldings around the window and doors. the other room just had to be spackled in some locations and crown and decrative moldings put up. we signed a contract at one price and i bought the materials including the molding. two days into the job the contractor told me he would have to charge me more because the molding i got for the windows and doors were not crown but decorative molidng, and he has to cut and measure, and they were much more work to put up. Should i pay more or should i refuse to pay more because the work order did not change, which was to put up crown molding and molding around the windows and doors?