non linear mapping help

I need to map a analogreading(thermocoupler) with 39k pullup to a Temperature value. This is for a 3D printers hot plate. I got a simple relay opening and closing when temp is lower or above 2 degrees. This board heats super slow so this relay only clicks every 3-4 mins or so. my issue is when i directly map my lowest pot reading when at ambient temp 25 degrees is 722. My highest value temp is 120 which reads 50ish (analog). if I map these values map(SensorIn, 50, 722,25,120); I do not get correct reading from ambient to top temp. so the temp, as it rises is not linear to the thermocouplers voltage increase.

for simplicity if you could explain this in a way where I can see it happening on serial monitor. this was on arduino reference for arrays, So If I want the computer to increment mySensVals but to print what

mySensVals is = to ...then what
myPins is = to

this will, in the easiest way, show me how to do this.. Thanks again!

int myInts[6];
 int myPins[] = {8,7 , 4, 3, 1,0};
  int mySensVals[6] = {0, 1, 2, 3, 4,5};
void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:



for ( mySensVals = 0;  mySensVals < 5;  mySensVals =  mySensVals + 1) {
 Serial.print("mySensVals-->  ");
Serial.println(mySensVals);
Serial.print("myPins-->  ");
 Serial.println(myPins);
}
}