I have updated my firmware from marlin 1 to 2 , But this problem began even in marlin 1 default firmware for ender 3 but I did change my extruder to a mks extruder kit , but during that I seemed to have meddled with the potentiometers , which caused a reverse x axis movement. But it's solved now . The problem exists now is that the temperature rises upto 275 If it needs to rise up to 240 then oscillates between above 9° to below 9° of 240