If an electron (photon) can pass through a gap smaller than an electron (photon) then it is a wave otherwise it it a particle. Is this a correct way of reasoning?
In the prevailing theories, the electron can be considered a point particle. There is no space too small for a point to fit through.
You are thinking in terms of every-day concepts.
A particle is like a baseball or a bullet, it travels through space until it hits something.
A wave is like an ocean wave that travels across a wide area, being everywhere along its moving boundary, expanding and diminishing until it becomes insignificant.
Physicists started out with concepts like these, and they used them while they worked. As the math got stranger they tended to keep using the old names for new concepts until it reached the point that they just don't mean anything like the things that the names evoke.
It's a little bit like economics, where the economists talk about complicated concepts with simple names. If you imagine inflation and GDP and national debt as things like potatoes, you won't get anywhere at all -- each name stands for a complicated statistical concept which only makes sense in terms of complicated statistics. People try to imagine simple rules for how they interact, and in reality the economy does complicated things that don't much fit the rules, and then we do statistics to come up with numbers that sort-of represent a simplified concept of the reality.
Similarly, electrons ARE complicated statistical concepts. They aren't very much like baseballs or bullets. They aren't very much like ocean waves. They just aren't going to fit into those concepts. If you try to think of them like potatoes you will be as confused as if you try to think about economics. Maybe more so.
You want a way for physics to make sense. But it just does not make sense. The math gets the right answers to statistically fit what happens. That's all physics does. There isn't anything else there.