Full page width needed

Hi
I have tried to increase the width of my main section contents by using the information at forum link https://ww.wp.xz.cn/support/topic/how-do-i-make-it-so-that-the-website-displays-at-the-full-width-of-my-browser?replies=2

My test site is fllodproblems.co.uk what am I doing wrong. there is to much space on the left hand side.