az530on21's

Hey guys. I need some help from anyone who has installed the Hamann Difusser. I took my car to the shop yesterday to have the exhaust and difusser installed. They called me and said that the difusser is slightly "bowing" out and the rubber cement that Hamann includes would not hold it in place. All the instructions say is to remove the old difusser, install the clips on the outside edge, and use supplied cement for the top piece. I am wondering if anyone else has had this problem and if there is any additional modifications, or clip adjustments that can be done to fix the problem. Any help is appreciated. Thank you.