I think a bit of blur on the aurora might soften those edges in the middle. You could use the 'blur object' function to achieve this (assuming you've shaded an object). I'd also add a bit of pink to the colour. I agree about the cottage roof. The whole foreground would be improved by a little more moonlight to bring out the detail, particularly in the trees on the right. If you use cool moonlight you could strengthen the light from the window to a bright yellow so that it's not lost. A great image! Good luck.