Door Problem

Here's the door so far. I'm really happy with the door itself and okay with the frame, but that top thing...put simply, it sucks.

 

I'm really unhappy with the blocky look the tiles give it (the arch should be smooth and actually be in front of the wall itself), it's too small, and just isn't very accurate at all.

 

On the left is a reference to how it should look (from Ray Keim's awesome Haunted Mansion paper model), and then there's mine. I put some notes in to give some detail on the problem spots.

 

I'm out of ideas of what to do here. Any suggestions?

Done