Both Audioguru and myself stated that the output is in the positive region, and you are saying the output goes into the negative region, even though you power the IC from a positive voltage? A series capacitor can perform that, however you do not say there is any component such as a capacitor.
In any case, if you want to level shift, the easy way is with a resistive divider. Adjust the potentiometer to shift your signal up into the positive region.
The 1M resistor is not necessary. It's there to indicate how the output signal is referenced to ground.