Storfront margin problems

You could use something like the following in Appearance->Customize->Additional CSS

@media screen and (min-width: 1060px ) {
	.site .site-header .col-full, .site .storefront-breadcrumb .col-full, .site .site-content .col-full, .site .site-footer .col-full {
	  margin-left: 0px;
	  margin-right: 0px;
	  max-width: 95%;
	  width: 100%;
	}
}

Okay, it works very well, thank you very much, one more question
How do I put the sticky menu in the header?
But only on the pc

Try adding the following CSS

@media screen and ( min-width: 568px ) {
  .site-header {
    position: fixed;
    top: 0;
  }
  .site-content {
    margin-top: 262px;
  }
}

You’ll most likely have to adjust the 262px value though to whatever the height that your header is currently. As you didn’t link a site, I wasn’t able to give a specific number.