Different image sizes Homepage vs Post on Mobile

Hello great Catch Team i have a little issue please take a look at this screenshot on mobile: https://www.dropbox.com/s/x7nb5x2rq9t393v/Photo%2009-02-2018%2C%2011%2006%2026.png?dl=0 As you can see the featured image on homepage is still beautiful and great on mobile Now please take a look at second screenshot on mobile too but inside the post: https://www.dropbox.com/s/gkb0ztcxe4c70c2/Photo%2009-02-2018%2C%2011%2006%2041.png?dl=0 As you can see image is not full width as per homepage. How can i make image same witdh inside the post look great like the featured one on the homepage? vitamineproteine.com