I bought a plastic headliner from classic industries, glued the fabric on and mounted it. But it won't sit flush against the middle so I can mount my dome light. How can I glue it to the roof where it will sit flush and not press against my headliner or how can I toughen where my dome light attached to the pins to how the pressure of the headliner?

 

On those ABS replacements the light lense holds the headliner to the roof.
Pretty cheezy tho as the light guts are pretty old and brittle.
My t-top ABS install I used a hidden trim screw with washer to hold the ABS roof in place.
Screw hidden by light cover.

 

I found that my truck uses heavy-duty Velcro,....... I'd bet that would work well on the aftermarket headliners too.