Hi,
Your plant might be sterile. Double Impatiens sometimes are.
Remy

Take cuttings and overwinter them indoors as houseplants if you don't have a green house. They will root easily in soiless mix, vermiculate, perlite, or water.
If your plant does set a few of the little football shaped seed pods you can harvest the seeds, but expect the resulting plants to be single, semi-double and double.
I would be happy with that in a casual setting but if you want uniformity for a formal situation you might prefer cutting grown plants.
You could also keep one plant indoors over winter and use it to start multiple plants from cuttings in early spring.
Alana

Sorry about all the typos in the above post tk. I must have still been asleep.
A

I've got to get out there and clip some cuttings before the plant gives up the ghost. thanks so much for the information. And your right I like the doubles more than the others.