Hold the fabric -- inside out -- against the lampshade, with the edge of the fabric against the seam. Wrap the fabric around and overlap the edges by 1/2 inch. Use the marker to draw a line on the fabric from the top of the lampshade to the bottom along the seam.
Wrap the top of the fabric into the lampshade and draw a line 1/2 inch from the edge. Wrap the bottom of the fabric into the lampshade and draw a line 1/2 from the edge. Remove the fabric from the lampshade. Cut the fabric out along the marked lines.
Spray a thin layer of glue on to the lampshade. Hold the fabric up against the lampshade the same way you did in step 1, except this time keep the patterned exterior outside and the marked interior inside. Press firmly while you stretch the fabric across. Apply glue to the extra 1/2 allowances on the top, bottom, and the seam. Fold them in and press firmly.