Idolise

I downloaded the drop shadow plugin but how do I get my shadow to reach the edge of the page? The width of the shadow is about 2cm and I need it to be about 10. Edit: If I untick keep original image it reaches the end of the page but then I cannot get it to feather as much as I would like.

Okay I'm making an image and I want to create a black border around a freely drawn selection but then feather it in so the opacity of the black border starts at 0 and ends at 100. How would I do this? Cheers.