How can i reduce the offset error of the error amplifier of my PWM generator?
Ok, we are closer to being to having the same understanding.  I started with the schematic in your question and created this simulation;



Here is the response with the schematic updated to match the photo and R3 changed to 30.3k.



I'm sure the components are better than 1%.

The plot says 5-vfilter because I used a filter block and subtracted the output from 5 to invert it.  I did not model the inverter or filter.  The inverter can introduce gain error the same as the error amp.