The border is coming from the file it looks like. The right edge has a bit of a white/gradient or something so getting rid of that will get rid of the border.
I changed your background for the #header to repeat-x so that it repeats across the entire area. If you switch out the image with a new one that includes the leaf border on the bottom and matches your background gradient you can keep the current css.
You may need to adjust the position of the gradient background OR replace it with one that matches where the leaf gradient will stop. Then, make your pages background color the same as where the background image ends and set the green to white gradient background to repeat-x as well (i've done this just now in your quick css just to save you a step).
Hope that helps :)