You will not be able to copy of line of boundary to the boundary layer, only polygon data can be copied. So honestly the only way to get your Boundary from the headland guidance would be to display as the top layer. Right click on the field name under the Red Barn Tab on left and select Edit Boundaries. Use the Include polygon tool button and trace around the headland guidance layer. Each time needing a direction turn, left and drag and until manually creating the correct polygon shape. Right click and select Finish. Click Save and Close.