Poster printing

I created a 9" x 9" square using NodeBox 3 using 96 dots per inch. Accordingly, the square was 864 pixels by 864 pixels. How do I poster print the square on 8.5" x 11" (letter size) paper such that it is exactly to size?

With further reading, does NodeBox export images at 72 dpi?

NodeBox's support for exporting is a bit weird, as it always add a small white border to the canvas on export. We'll fix that in an upcoming version.