Did the seeds sprout at all? New Guinea hybrid seedlings seem to need slightly warmer temperatures to survive.

New Guineas shouldn't be treated the same as regular bedding Impatiens. They prefer more sun and are more senstive to soil that is too wet or too dry.

The best way to get new plants is to cut off stems a few inches long, remove the bottom leaves, and place in water. They should get roots in about two weeks, then plant them. You can also plant the cut stems directly in potting soil, but they are very prone to rotting.