I'd recommend using a carpet knife to do your trimming. Maybe a brand new razor blade here or there.

Nothing duller, like a utility knife is way too dull even new, imo.

Like the knife on top, double edged sharp as heck, way sharper than the other one even with a brand new blade. I just got done cutting drywall with it in this picture, it works great on all kinds of stuff.

You want clean cuts and don't want to be hacking away at it. Be ready to change blades often too.