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If you go to Object menu > Fill and Stroke > Stroke Style tab > Width, you'll see that your stroke width ('stroke" is what Inkscape calls the black border that you want) is 152.4 mm wide. If you make that much smaller, I think it will display more appropriately.
If you use the spinbox (the tiny up/down arrow on the right of the number) you'll see the stroke will change immediately. If you change the number by typing, you'll have to press Enter or click on the canvas, to make it take effect.
