My but are we not high maintenance today !
Since you'd be butting trim, use one "leveled" long trim piece temporarily screwed onto the wall as a "ledge" to rest the bottom edge of the Sintra on. I usually will then set the Sintra up and get it centered where I want it to be, then using a pencil, go around the three free edges and mark off the perimeter. Take the Sintra back down and lay it face down onto a clean, scratch-free surface. Apply adhesive to the board first, keeping at least 2" clear of adhesive all around the outside edge. Apply adhesive with lots of small, 1/2 your Pinky-thick continual beads...and only try reach in far enough to do one half the "height" from one side then jump around and do likewise. use a Square Toothed Adhesive Trowel (...$3.00 @ HD..) to spread out and merge most of the rows of beads. DO NOT OVER WORK IT! Your just trying to equalize the height of the adhesive beads.
Then go to the wall and apply a ring of adhesive 1" inside the Penciled-in perimeter. Trowel it out toward the Pencil line and in toward the center. But stop short by 1/2" shy of the pencil line.
Some do apply all the adhesive directly to the wall only. If you have two Caulk Guns (...smooth flow type...) and two people, the job goes really quickly.
"TWO" people then pick up the sheet and set it carefully onto the "ledge" If you can have a 3rd helper, that allows him to gently push in the bottom edge so it get's onto the ledge easier. (no bowing) Otherwise, when you pick up the Sintra, both of you must purposefully create a inward bow to counteract the Sintra's tendency to bow outward.
And then...if you do have a 3rd there, also have 3 Clean soft towels available. have your 3rd start pressing against the bottom of the sheet at Center, and sliding side-to-side, press the Sintra FIRMLY against the wall in a sqeegee-like manner. Let the 3rd gradually press the Sintra onto the wall from Bottom to Top, like you would apply a decal.
After it's up, everyone press the 'ell out of the Sintra using sliding pressure. Don't forget to concentrate around the edges to "set" the outside beads.