Assigning pen style enlarges 24x36 sheet to 35' or 75' long, not 36"

Hi, I'm using V5.1 on a Mac.

My issue:   When I create a 24x36 sheet and assign a ctb pen style, it comes out 35' long, not 36" (one sheet comes out at 75' wide).  I determined this by measuring with the dist command in paperspace.

When I created an 11x17 with the same pen style, it worked fine.

I tried duplicating that one, and modified only the sheet sizes to 24in x 36in.  Same issue.

I did a new test one without assigning a pen style, and it worked, but not assigning a pen style means I can't print anything worth having :-(

Help please!