There are a few things you can do to help you determine if the problem is in your code or in your wiring.
You could try sending serial messages to the Arduino serial monitor to see more clearly what your software is doing. For example, print the LED that you want to light and the pins you your are setting to control the multiplexer.
You could also write a simple test routine that ignored the pots and just sequenced through the LEDs to see if the wiring is the problem.
I hope that helps.