Error printing large scale on multiple sheets

good morning. I am trying to print a large (C size) paper on multiple sheets of standard letter (A size) paper. I am using the poster option at 100% and am getting 6 pages printed out with guides for the overlap. However, the printed version is not to scale. I have checked the PDF file and everything is correct at 10" x 13.5" (according to Adobe Reader DC) but the printed version is not.

What am I doing wrong? or not doing right?