How far from the Sun is Pluto in your model? Every planet sits at its average distance from the Sun, scaled from this one number. Pluto's average distance is 39.5 times Earth's.
Seconds for the True size and Zoom to fill buttons to take Earth from true size to filling the screen. Every planet zooms at this same speed.
Hold a credit card or driver's license against the screen, turned so its short edge runs across. Slide until the outline is exactly as wide as that short edge.