Hi Babs,
For the most part, I actually fixed the top edge of the backscene with double sided tape to ensue it was in the right place / lined up with adjoining sections. Then rolled the scene up and held it in place with a cloths peg or similar, then applied the adhesive directly to the wall from the bottle in a criss cross pattern, and around the edges. Then lowered the scene down, pressing it against the wall as I went. Unfortunately, in my case, the top of the wall has a joining strip that hides the join between wall and ceiling, and several vertical joining strips along the wall, so nothing was completely flat which resulted in some visible creases , but overall, I'm happy with my results. On a completely flat backboard I'm sure you can get better results.
It does dry quickly, but you still get a couple of minutes to adjust, but that's why I went for the pre-fixed top technique so I didn't have to spend too much time getting it in place.
Good luck with yours
Regards
Alan