head picture full width

Hey there,

I’m using twenty fourteen, installed the extended plugin, and removed the sidebar and changed it to full width. Now my displaypicture at the top of my side is not full width. It seems like it is shifted to the left since there is a blank space area to the right.

I already changed all the numbers to max and 100% as well as I used a child theme with these codes:
Code:

.site-header {
background-color: #000;
max-width: 100%;
position: relative;
width: 100%;
z-index: 4;
}
.site-content .entry-content,
.site-content .entry-summary,
.site-content .entry-meta,
.page-content {
margin: 0 auto;
max-width: 100%;
}

or

.full-width .site-content {
    margin: 0 auto;
}

.full-width .site-content .has-post-thumbnail .entry-header {
    margin: 0 auto;
}

.singular.full-width .site-content .has-post-thumbnail.hentry {
    margin: 0 auto;
}

.site-content .entry-header,
.site-content .entry-content,
.site-content .entry-summary,
.site-content .entry-meta,
.page-content {
    max-width: 2000px

}

.hentry {
    max-width: 100%;
}

.site-content {
    margin-left: 20px;
    margin-right: 29%;
}

But nothing worked so far. I searched in the web for hours already but couldn’t find an answer, any ideas?