Word background image does not scale to page

[neelyrock]

I want to have background that does not print and thus I'm using Page
Color -> Fill Effects... -> Picture Tab to insert my background
image. However when I zoom in or out in the document, the background
image gets all messed up (in relation to the size of the page). My
goal is to have a reference image for a sheet of preprinted labels so
that users can understand where their address will be in relation to
the image on the labels (but not print out this image as the labels
already have it on them).

I've read about possibly using a watermark to get what I need, but I
don't know how to keep that from printing. I do have an option that
says "Lock picture aspect ratio" which also sounds promising, but it
is grayed out and I don't know why...

Thanks so much for any help!