Bathroom fan wiring

I am trying to install a bathroom fan and am having some issues. The sketch below is how I curently have it wired. (blue in the sketch are the white wires) Previousy there was a single switch that controled the light. There were only 2 wires from the switch which I folowed to the high ceiling but not farther. I think they are the hot black from the main circuit and then the black from the switch to the light. Currently, the light works perfect using the top switch, but the fan doesnt turn on. I am not sure what happens to the wires above the high ceiling. I added the white wire between high and low ceiling to connect the fan white to the light white. Am I making a wiring mistake?

Thanks in advance!