I am not speaking on behalf of GCU as I am not sure about their affiliate program.
 
BUT other POD sites to be an "affiliate" the link must go to the store front as a "whole". That is the purpose of being an affiliate. You are trying to get customers to the site itself where they may purchase someone else's designs.  
 
If the customer is taking the link from your site - they more than likely will continue on by searching your name. If you make a direct link to your product from your site, it is no longer considered an "affiliate".
 
As I stated, this is the general overall POD affiliate programs "rules."