Spray carnations have long stems with several short laterals off that main stem. Separate the flowers apart and use them to good advantage by inserting them around the entire arrangement.
Keep some blooms on the long stem to use for both of the long ends of the design.
This is what the first stem looked like after I removed the shorter laterals from the main stem.
I inserted the one solitary bloom into the bottom right and had the flower extend beyond the greens.
I took another stem and removed all the laterals but these two.
I then inserted them on the opposite side from the first carnation.
I now take another long carnation and insert it on the first right side.
See how I spaced it to the side and apart from that first long miniature carnation.
Now the right side is a rough "mirror image" of the opposite left side.