You are already wrong. Photons do not work like this. Instead, it is an EM wave of a certain energy and frequency that is emitted and propagates towards the screen. When the wave interacts with something, and by that I mean when it actually transfers energy, it will do so in little discrete amounts that we label as photons.
What sophie is trying to get you to understand, and what he has pounded into my head previously, is that you cannot say "a photon approaches the screen" or "what is the size of a photon". A photon is simply not a little particle that would behave in this manner.