That's what I did - Looks as if you have made your Home page narrow in the expectation that it would fit smartphone. It won't automatically.Later:
....Which is what I did after reading the link from Post 8 - have read a bit about mobile websites but never come across that before - thank you.
Anyway in practical terms.... for iphone 6 ....375px x 667px (and really all small group phones) the NOF page needs to be set to around 1000px x 1750px to fit the screen. The text on the pages is then increased in size to between 36 and 48px to display properly.
To clarify, the text is NOT automatically increased in size.
You have to have two versions of the website - one desktop (and ipad will be ok with that) and one for 'smaller' devices. The text needs to be sized as stated AND the line spacing needs to be changed accordingly (via CSS or Style). Images also need to be resized to fit the smartphone device (eg 1000px if you want to fill the width of the smartphone). Not sure why you want to set at 540px....1000px looks fine on all smartphones.
I have created several mobile versions (in addition to original post) including:
http://www.lookinggood-aberdare.co.uk
and http://www.libertybs.co.uk
Two versions means you can vary things like menus on the smartphone version (which you cannot do on all these 'responsive' websites).
The only downside is that you have to maintain two versions - in your case eg if you add/delete products.