Posted: 17/07/2016 at 22:50
If you still have your seed packet, check the variety. If it is an F1, it will not seed true.
Otherwise, let the flowers form seed, when they are Brown and dry, save them in a paper bag, not plastic, to sow next year. Letting the seeds form early in the season will curtail flowering.
I would try and get another packet of seed for a quid.