Canvas size and print files

Hello 

I made a T-shirt with 25cm x 27cm printing area. with 300dpi I had to make the canvas 6800px by 6000px in order to get printable exportation files. I used CSS to fit it in the webpage and it worked. 

However, in phones it's not loading due to it's huge size (I guess).

I also have hoodie with 9462px by 8342px canvas and it's not loading as well 

is there a way to solve this? or to separate the canvas size from the exportation size(actual size)? 

Help please

Thank you