I am trying to model behavior of UC3842 PWM controller https://www.ti.com/lit/ds/symlink/uc3842.pdf
By information from the datasheet done a crude model of loop behavior, But as you can see I have not used error amplifier or without matching the open loop gain given in datasheet If I change any of the gain or offset or sense resistor I wont be able to expect required output. Is there any specific method/documents which may help or sensible approach to take this model to next level.
There is available on the web the model of this device in Spice, which at first glance may be a much more reliable approach, which would save you from a lot of time, just to validate your model. If your above simulation tool (I didn't recognize it) doesn't support such a feature, you can just use the spice netlist file as a start point to build your own by hand circuit.
use the LT1243 by linear.com in the free download LTSPice simulator...it is pin for pin compatible
I attachch an ltspice sim of it for you
Change it to .asc and run
PSIM has a model of UCC3842 as well though you'd probably need to pay either to get it or to get much use from it (Though if you have a budget I highly recommend PSIM).
If LT1243 is compatible however then using LTSpice is a no brainier. LTSpice is free but also arguably the best spice tool out there.