The single photon registers in a single spot on the screen, as a particle should, and so there's no problem with assuming that it went through one hole or the other.
The fun starts when you start sending single photons through the holes one by one - again, every photon registers in a specific spot; but when taken in aggregate, those spots form the same interference pattern as with multiple photons.
The fun starts when you start sending single photons through the holes one by one - again, every photon registers in a specific spot; but when taken in aggregate, those spots form the same interference pattern as with multiple photons.