Materials list for Deck in Landscape & Deck listing thousands of boards?

[SteveDr]

I'm new to using the program - I've put together a first try at a deck design, but when I select the deck area in a rectangle and calculate the materials list for the selected area, it lists over 4,000 boards. I've attached a picture of the floor plan and the materials list. Am I doing something wonky, or am I just not reading the materials list correctly?

Thanks