Did you carve the dome out of styrofoam yourself?
I bought a 10" hemisphere at my local Michaels craft store, about $12 if I remember right. I had to carve out some of the top center where they make it with a flat area, and I also cut out a 3/4" section down the center to make it oval and fit the helmet sides. I did this because initially my plan was to do paper maché over a mold like I did when I was 12 but it wasn't working well.
Even after some sanding the result is not flat enough on top, so I need to sand it down to the right shape. Another issue is that most spray paint dissolves styrofoam. I applied several coats of water-based primer to prevent this, but it still had some pitting where the spray paint solvent soaked through. When I sand the top down I'll patch and fill those areas.
Here are a few pics of the dome modification process:
I noticed that you've removed the visor T from your build up. Usually folks leave that in until the end, makes the helmet easier to work on and stronger, and helps keep the right shape. I'd add in some sort of bracing instead on yours to help keep the shape. I used toothpics at one point for this, not very effective.
It took me 2 tries to get the cheek shapes to work reasonably well. The first try I made the cheek assemblies prior to installing, but found they didn't match the cheek outline well. So the second time I fit the arches first, then fit the cheek inner surfaces. This worked much better but is still difficult.