It could be due to hot air from heater core is mixing with cool air, you should not have topped up the gas...
After the incident your mechanic might have connected the heater core pipes...
Now remove the extra gas by checking the pressure according to the ambient temperature and either disconnect the heater core or get the ac hvac checked and repaired...
@aziz.rehan is right. You should confirm if the temperature sensor is sending correct reading or not...
Do confirm the cap pressure if it is .9 or 1.1 bar.
Remove the pipe from both expansion bottle and radiator check if clear... and check cap for cracks...
You are in lahore, right?
Why dont you visit @syncview? Call him tell the problem, take appointment, visit him, and take back the car problem free...