Images are in pixels on the computer, not inches. Inches can be specified as whatever you want when you print it out. Your image is only 1600x1200 pixels, which is only going to give you 47 dots per inch. I think you should redo this in higher res, first off. The second issue is that your image has a 1.33 : 1 width to height ratio (like most monitor resolutions.) But you want your printout to have a 2.125:1 ratio. For this image that means you either have to cut out over 37% of the image height-wise, or you have to stretch the image horizontally and distort it significantly.
I would just recreate the entire thing, with image dimensions of at least something like 3400 x 1600, giving you your proper printout dimensions, and 100 dpi at least.