What is this
You are correct in your identification of this flowering plant as an impatiens. All impatiens have five petals and three or five sepals, with the lower sepal elongated into a spur in most species. Within the impatiens species, this lower most sepal has been greatly modified and elongated into a nectar filled spur. These spurs in some flowers can be very showy like that of I. niamniamensis 'African Queen' with its candy corn colors are shaped for bird pollination; whereas, the spur in I. walleriana have evolved specifically for moth and butterfly pollination.
It is this showy, nectar filled spur (sepal) which caused you confusion and most likely that species you have growing is one of the Impatiens walleriana cultivars.