Illustrator Help - Saved File Uploading to Printer as "pin size"!!

First, THANK YOU @danlovesadobe for the AMAZING videos! I am fairly new to Illustrator. I have followed the tutorial for beginners step by step to create a print to have printed for T-shirts. I make sure to create outlines for everything. I save the file as a PDF. Looks good in my saved files. When I try to upload it to the printers canvas, it is coming out pin size! If I open it in any other program besides Illustrator, it is coming out pin size. What am I doing wrong? I have worked in Inkscape and a design program before, so I am not completely new to the concepts. I have tried everything to figure this out - for the past week!! Any advise would be greatly appreciated!!!