Managed to fix it in.
For anyone wanting the same here is the code:
<!--city-->
<container class="horizontal_adaptive_container" gap="0" mode="distribute_equally" height="648">
<container default_width="-1"/>
<container default_width="1080">
<layout class="stick_to_sides_attachment" apply_to_children="true"/>
<widget class="background" file="backgrounds" id="bgnd">
<layout class="stick_to_sides_attachment" alignment="all" apply_to_children="true" inset="0"/>
<record id="object_property">
<record id="default_properties" image_alignment="centre" scale_picture="true" keep_aspect_ratio="true"/>
<integer id="get_property" value="bgnd" />
<integer id="set_property" value="file" />
</record>
</widget>
</container>
<container default_width="-1"/>
</container>