The helmet could be a tad bit small. But if its just the paper ring that sticks inward thats holding you back, it wont be a problem. What I would do is follow through with hardening the helmet, then trim the hole down. If you harden it first, the helmet has better odds against warpage (did i just make that word up!
). I recently did a Clu helmet from tron, and had the same problem. Anyhow, your helmet looks great! Is that your first build? I want to see more of that helmet, more pics pwetty pwease!