1) How many data points did you use to plot the current vs output voltage?
2) How did you obtain the value of current? Using current meter? Or, based on the calculation of V (across Rsense) / Rsense?
3) What is the value of R1 and Rsense?
4) What is the 'current (PWM)' in the schematic diagram? I think a variable voltage source should be connected to Rsense so that various current values can be obtained to produce various voltage values from opamp's output terminal.