Oops! You should not have had to cut that piece off. It is a flap that is supposed to fold and tuck up under the opposite edge of the groove. The groove in the gasket along the bottom of the window looks like it should have a locking strip, right? Not so, the flap tucks under along the bottom edge, and the locking strip begins where the flap stops. There is not enough room in the groove for both locking strip and flap.