If you've correctly aligned the adhesive, the edges will fall perfectly into place.

If your adhesive is slightly misaligned, gently pull the long edges into alignment with the frame.

If the adhesive begins to crease or wrinkle, remove it and start over with fresh adhesive.

If you don't have another set of adhesive strips handy, it's okay to temporarily put your iPhone back together and use it normally without any adhesive. Just keep in mind that your iPhone's water resistance will be compromised until you replace the adhesive.