Did you seed a dwarf variety? These can be maintained under 8 inches, flower freely, and can be maintained in 4-inch pots. They seem to be more popular in the United Kingdom; you can see mention of them here: http://thepelargoniumregister.com/horticulture-symbols-and-terms/ They might be able to provide some info.
If you are growing standard size, you might need to keep it pruned.
Did you seed a dwarf variety? These can be maintained under 8 inches, flower freely, and can be maintained in 4-inch pots. They seem to be more popular in the United Kingdom; you can see mention of them here: http://thepelargoniumregister.com/horticulture-symbols-and-terms/ They might be able to provide some info.
If you are growing standard size, you might need to keep it pruned.