Trying to make a faded border

[DiarmaidB]

Hey, so I've been searching for this for while now, but all I can find is the opposite of what I need. 
I have a border all around the edge of my canvas, with nothing inside it, and I want to fade it, so that it is 100% visible at the outer edge and 100% transparent at the inner edge. 
Here is the image I am working on (Image 1) and an attempt I made, using the gradient tool, which is similar to what I want, but not perfect (Image 2): 
Image 1Image 2

If anybody can help me out here I'd greatly appreciate it 🙂