The end panels are the remaining two 9" x 14" panels. Place one end panel at the end of the assembled pieces and use the 11" x 45 3/8" board to align it with the front of the inner panels (see first photo). Now mark the location of the top and bottom ramps on the end panel (second photo). Drill 1/8" holes 2" in from the ends of the top and bottom ramps as marked on the end panel (you should have 4 holes). Drive a 4d finish nail into each hole from the side opposite the markings. Only drive the nails in until the point sticks out about 1/8" from the marked side (third photo). Now place the end panel back on the end as you did to mark the panel and press it into place letting the nail points mark the top and bottom ramps (fourth photo shows mark). Remove the end panel and at each marked location on the ramps drill with 1/8" hole about the depth of a 4d nail. Put wood glue on the end panels in the area marked for the ramps (fifth photo). Place the end panel back on the assembly and nail into place. If you were real careful the nails should follow the drill holes and not split the ply wood ramps. Repeat this process for the other end.
NOTE: This step is tricky. Be very careful to drill all holes as perpendicular as possible. If the holes not aligned well you risk splitting the ramps which could cause the cans to get stuck and not roll down the ramp. Since the end is getting glued you could potentially just use small brads to attach the end and skip all the drilling, but that is not how I did mine.