I just bought a 2004 Mustang convertible and can't seem to install the boot covering the ragtop. I've had it laying flat in the Florida sun for a week but the creases are still not perfectly flat. I've managed to fit it in the back and side slots. I can snap down the sides. Now I can't get the tongue into the slot on the back of the rear seat. I've been fighting this for more than a week and would appreciate any suggestions. Thanks, Bill