Continue peeling the back liner off of the adhesive while pressing the adhesive into place along the edges of the iPhone's frame.

If you correctly aligned the lower edge of the adhesive, the side and top edges will fall perfectly into place. If the adhesive is misaligned, remove it and start over with new adhesive.

If your adhesive is misaligned and you don't have another set handy, it's okay to temporarily put your iPhone back together and use it normally without any adhesive, but keep in mind that your iPhone's water resistance will be compromised until you install new adhesive.