Plastic 36'' L End Cap in Black

I had purchased this to replace a 2 year old item of the same make/model that had begin to tear and was no longer serving its purpose - namely seal under the front door. Unfortunately, and I have no idea why, this new item still leaves a small gap under the door after installation. There's no chance it was installed incorrectly, so it must be somehow different from the original even though it has the same part number. Had to purchase a different solution to seal under my front door.

It is what is said it was. I just messed up and bought the wrong thing so I have to return it now