I am creating vector images and setting the final size. I then select the properties in my printer to print to poster. It prints to poster format, but the output is considerably larger than the input. In other words, I had set the dimensions to about 12" wide x 15" high, but when printed and taped back together, the result was about 15" wide x 18-1/4" high (about 1/4 of the original size greater). Where do I even begin to fix this problem?

Some specific details which may or may not be of assistance:
file type is PSPIMAGE
image type is VECTOR
72 PPI
RGB 8 bits/channel
1 layer

PSP Printer settings
orientation 1
fit to page

Printer Canon MX80
media type plain paper

print quality standard
portrait
paper size: standard
layout: poster printing

One of my files uploaded to play with if needed. Currently set to about 9.25" wide x 12" high

• http://files.engineering.com/getfile.aspx?folder=40c4a3e2-fd62-404e-92a9-c4