Twenty Fifteen, having trouble on browser to mobile transition.

So the way i’m designing this website, it’s all looking in order on when opened on the browser, with the sidebar where i want it. on the side. But when i try to open it on mobile, it looks hideous and because the sidebar is moved to the top, anyone know what i can do to make the mobile version closer to the broswer version? even if that means having to scroll around the mobile version left to right. here’s the site so you can get an idea what i mean.
https://www.murphdogconcrete.com

any help would be much appreciated, thanks!