Hi if you dont want to change the structure of the template you can add this css rules
.page-id-21 .single-page{
margin:0;
}
.page-id-21 .single-page .single-content{
margin-left: 25px;
}
I added a .page-id-21 class, otherwise in the contact page you will add a margin. This can be a solution, another is to search the correct template page, if it's a premium plugin it will have it, and you dont need to add the css rules.