Casting from iPhone or using Stream app from Firestick or a Roku won’t give full screen

I just installed the Xfinity stream app on my Firestick in my living room TV, my Roku stick in my basement, and casting from my iPhone max to my bedroom TV. 

all TVs (different models and sizes) are showing in the center of the TV with black boarders, instead of screen.

this is THREE different sources (Roku, Amazon  Firestick, and IPhone) to Three different TVs, How do I fix this?