The loop appears to be doing limit-cycle oscillations. When properly stabilized, the unit will operate with a constant output pulse-width with a steady output voltage regulated at Vref. The only ripple will be due to the 200kHz switching frequency.
How did you simulate the loop? Can you post your simulation loop with parameter values? Was the PWM simulated with a linear gain block? If you used a gain of one for the PWM gain block, that likely will give you an incorrect simulation, since a PWM generally has an input-to-to output gain significantly greater than one. This PWM gain has to be calculated from the PWM internal chip parameters and the ratio of the input to output voltages. It is not explicitly given in the data sheet
Also state the R & C circuit values and input and output voltages for the circuit.