Hi Scott,
It is contained in your header container.
To make it full width completely, you can add this under Custom > Edit Global CSS in the Customizer.
@media (max-width: 979px) {
.x-navbar .x-navbar-inner > .x-container.width {
width: 100%;
}
.x-btn-navbar.collapsed {
box-shadow:none;
}
}
Hope that helps.