Help after the fact is useless but to help you going forward only but Headliner material, foam backed. I use 3M Super Trim Adhesive in the Red spray can. I'm assuming the headliner core was rigid Styrofoam. After removing all the old form from the core you spray 2 good coats of glue and 1 light coat on the backing foam of the fabric itself. While still wet I use spring clamps to hold the fabric around a piece if 1in PVC pipe on each side of the backing long ways. With help holding the fabric right over the top I gently press in the center first slowly working without stretching outward till in smooth to the edges. Working wet on wet repositioning is possible within reason.
If I die from a Deadly Sin it will be Gluttony!
"Formerly known as rojoguio"