I continue tucking in more rose heads on the sides, but I use small heads than in the center.
I'm going to choose tighter buds for the outer ends of my corsage.
This stem is going to be longer because it will slide under the center heads and still needs to be attached to the silicone pad.
You will have to judge how long the stem needs to be by eye placement.
Hold for a few seconds to all the glue to become tacky and adhere the flower head in place.
I even tend to spread the glue on the head itself if I want it to stay in a particular position.
Just be sure the glue doesn't extend beyond the pad or leaves.