U-Channel window seal length / sizing

[Builtlikeatank634X4]

Hey hey .. So I got a window seal kit .. Pretty universal and I'm doing a practice installation and the u-channel piece is long for my window with a vent.

Youtube videos only show installation procedures and I need to cut mine to length and reuse my retaining clips. I still have the u-channel I removed but the felt and material was wasted so I'm not sure how well the fit was and did it provide a good seal

Any help with a length to cut and should the ends be sealed up or sewn shut to prevent metal exposure or material being cut from metal edge

A good seal and fit helps .. Green line is extra channel to be cut off

Thank you for any help