Printing Size is wrong

What the print preview is showing you is the current image dimensions for the document (which is originally set by the Image > Image Size command) on the currently selected paper size. If it is showing an 8.5 x 11 inch image on an 11 x 17 inch sheet in the print preview, you must not proceed until the image size is corrected. There are two ways to do this. Either:

Scroll the options on the right side of the Print dialog box until you see the Position and Size options. If you just want the print to fill the printable area, select Scale to Fit Media. If you want to set a manual size, make sure Scale to Fit Media is disabled and enter the dimensions you want for Height and Width. This will change how it prints, but will not change the dimensions recorded in the image file.

Or:

If you want to change the dimensions of the image file, click Done, then choose Image > Image Size, set the width and height there, click OK, and save the document. Now the change in dimensions is permanent and if it matches the paper size, you should not have to change it in the Print dialog box. 

A couple more things:

Note that my image has empty white space on the sides. This is not a Photoshop problem, it is a mismatch between the proportions (aspect ratio) of 8.5 x 11 inches and 11 x 17 inches. 11 x 17 is a wider aspect ratio. If this image must fill an 11 x 17 print size, either the original image must be re-cropped to match the aspect ratio of 11 x 17, or the image must be enlarged so that the sides reach the edge of the page but that will necessarily crop out the top and bottom.

Also, in the Print dialog box, watch the edges of the preview and the Position and Size dimensions, because on most printers, the image will not print a full 11 x 17 edge to edge. There may be a slight margin, marked in the preview by diagonal lines. If you want the print to be edge to edge with no margins, this must be set in the printer driver software, not in Photoshop. Click the Print Settings button and specify a paper size that is borderless. For Epson printers it will say Borderless in the paper size name; I am not sure how it works for other brands.