> Please let me know how to set the testbench to find amplitude and phase mismatch ?
To examine the relative phase of the I and Q components, I believe you will need to create an expression that subtracts the two phases to compare it to the ideal phase quadrature. This can be done using the cross() function about your switching threshold. By computing the cross() function as a function of waveform cycle for the I and Q components, you can subtract the two to get their relative phase as a function of cycle number.
For the amplitude, you can use the calculator functions ymax() and ymin() to determine the peak-to-peak amplitudes.
I hope this gives you some help.