[Hollow box with inner and outer wall]

Hi, 

 

This is the first time I've ever used the 3D printer or cura on our site. I am trying to 3d print a small box with no lid, and no bottom, where the infill is only between the inner and outer walls. However, the machine keeps printing a small ring around the outside where the outer wall is, and then infilling everything inside the inner wall. Any thought how to stop this happening?

 

Thanks,

 

James

Chock Holder Single.stl