Can't complete construction tutorial

[Deezle]

I placed my static core before I started the construction tutorial.  When I came back to do the tutorials, I make it to the part where you place the core, but I am not allowed.  I can see the green zone but get the message you are not allowed to place any more cores or something to that effect.  Will I have to remove my structure and industry items to finish it?  The only reason I would is I can't place a second core on my current base.  I'm not sure if we aren't allowed to expand on sanctuary.