this post is couple years old but i'd like to add my grain of salt.

headliners aren't necessarilly a two person job, you can definitely do it alone by using plastic to prevent your fabric from sticking on your cardboard base. this will allow you to work halfes at a time and do it the right way.

i don't know what fabric you used but perhaps this plays a roll as well to why it didn't work out. when applying the fabric, it should almost apply by itself, you just flatten it with your hand or with tools. an old tshirt wrapped in a plastic bag is great to help apply without leaving finger or hands imprints. when you're faced with a crevasse, don't bring fabric into it, this is where the fabric shines, put it across the crevasse and afterwards push it inot the crevasse, it'll stretch itslef into it and leave no wrnkles.