Please try to use one of the shipping examples so that we can sort out any problem with your code. You can use an example such as "Cont Acq&Graph Voltage-Int Clk-Analog Start" . You can go to Help>>Find Examples>>Hardware Input and Output>>DAQmx. Tell me if you still see a discrepancy between the two graphs by using this example.
This can happen when you have a set up your terminal type to differential but you use a grounding terminal that is not associated with that AI block.
you can move your grounding terminal or change your terminal type to RSE.