sagging roof

i put valor style matereal in my whole int. it looks awsome with my silver trim except my roof is sagging and its only been on for 3 weeks, what should i do? take it back off and reglue it, if so whats a good glue to use, i use fabric glue last time and it doesnt seam to hold on the cardboard well, even though it holds excellently on the doors and dash

i reupholstered my roof not too long ago, I got this stuff called craft glue from wal mart in the fabric department. I havent had any problems yet. Its just kind of a b*tch to work with because its a spray glue, so you have to be careful not to spray it on your fingers and then get it on your fabric. I only did this a couple months ago though, so I cant say if it lasts forever. it seems pretty good though.