You'd be surprised how well pre-modern people were able to accurately construct big monumental images and structures on the ground that are best viewed from the air! A triskele would be perfectly achievable even without fae assistance or magic. I imagine such assistance would simply make it easier and faster.

Do you intend to draw the actual layout of the maze at some point? I have a thing for mazes (I posted one here once) so I am very curious to see it.