You might need to pry the cylinder the pin goes in in the opposite direction of where it’s trying to trend. E.g., if the two pieces’ cylinders don’t want to line up, you probably need to pry them over so that when the pin is in, they sit flush. This might be counter-intuitive. You might think you need to pry them together, but that will cause them to sit farther apart when the pin is in. Pry them away from each other, just a couple mm, so when the pin is in, they are closer.