Thanks for the font Mouse, I've found several that don't curve properly, it's a bit of a pain isn't it.

Have you tried copying you're moon layer, and flipping it, then moving it down onto the water? You can play with different blend modes, and opacity settings this way, and come up with some interesting reflections. I don't know about gimp but PhotoShop has some perspective tools that also work great for getting it to lay down on the water... Just a thought, but what you have here looks good too.