I agree with Don - use the groove, it's there for the placement. I use a white glue dirivite called "Jewel glue", a craft glue with various actual uses.
Also, if one side does not conform and stick, DON'T PANIC! Leave it and consentrate on what does stick, hold it down and make sure it settles. Go back to the other side when that has properly cured and just hold that down. Otherwise you'll make a semi-transparent mess.