Paint.NET :: Black Border Be Placed Around Edge Of Canvas?

I have some small rectangular drawing of different sizes (about 3" x 4" or 5" at 200 pixels/inch).
I want to place a simple solid black line border around the edge of the canvas. These drawings have a white background.I do not want white showing past the outside edge of the border.I want the border to show with an even smooth width on all four edges of the drawing.I want to specify the color and the width of this border. Here is what I have unsuccessfully tried: Using the Rectangle or the Line tool on a layer assigned for the border is a hit and mostly miss proposition.

For the Rectangle tool, once the rectangle is placed on this layer, I do not know how the adjust this rectangle. I erase the rectangle and try again. Sometime what I see is okay, but most of the time what I see is irregular and poorly positioned. For the Line tool the lines drawn often show as a stepped line, not a single width line. I do not know how to not have these steps occur, and I of course do not want curved lines. Can you instruct me about how I can create a simple solid black line border around the edge of the canvas?