Page format

Is there a way to set the page format?

I'm beginer of DW and I'm creating my first page.

Now my page seems too little (look at my firs image below) in the retina screen, in smartphone look ok.

I don't remember exactly but a few days ago it looks like the second image below, I mean from web, in local is alright.

Maybe some file is corruct (css or whatever) or I miss something.

Is there a way to set for computer a page that look like the second image below?

Thank you.

First Image:

Second Image: