Making an adjustable resistance
Using the pot like this is fine. Usually, when connecting a potentiometer as a variable resistor, you connect the unused pin to the wiper. Makes the circuit diagram look a bit cleaner, and in audio circuits keeps the pot from making scratchy noises while it's being turned.

For sensing ambient light level, this calibration arrangement should be fine.

Also, just a few schematic-drawing tips: Signals/information should tend to flow from left to right, while voltages should tend to go from top to bottom. Like so:







simulate this circuit &ndash; Schematic created using CircuitLab