The grating material is “etch”, but there is no material to be etched, so the refractive index is constantly one (the background index). You should change the grating material or add another object that can be etched into so the grating structure will appear. You can check to see if the geometry is correct by placing an index monitor over the structure before running the simulation.
Also, it looks like your symmetric and anti-symmetric boundaries should be switched, so that the electric field (blue arrow) is parallel to the symmetry boundary, and normal to the anti-symmetric boundary. See this page for more info on how to set up symmetry boundaries:
Let me know if you have any questions.