How long do you want the table runner?
what about cutting a background piece (like a cream, white, or dark, depending on your other fabric choices) at least 13" x 36" and laying out the pumpkins next to each other until you like the spacing between the pumpkins and around them. Then add a small border - either just a plain border or a basic piece border (squares, triangles, etc.) or even finish with prairie points. If you don't want it that long, adjust the length so that you're only using 2 pumpkins.