I was a bit impatient when doing the contact cement – didn’t let it dry enough so actually, it never had that instant bonding.  Instead, I use a heat gun to heat up both surfaces to dry the contact cement.  I still had 3-4 seconds to move the pieces around if the initial alignment wasn’t perfect.

for rounding over the edges, I used sandpaper and hand sanded the edge. worked well enough.

I’m really glad I bought the headliner.. looks great and does a great job of eliminating condensation…we went camping and there was quite a bit of condensation on the window but none on the headliner material.