Linear Actuator Position Control Reed Sensor

Using Arduino Motors, Mechanics, Power and CNC
7

You don't understand the difference between assignment of an existing
variable and declaring a new variable:

 if (Extending == true && CurrentPosition > goalPosition ){    
         //we have reached our goal, shut the relays off
      actuatorStop();
      boolean Extending = false;  ///////// WRONG!!!!!!
      Serial.println("IDLE");  
                 }

Declaring a new variable of the same name will do nothing. Assignment
(ie changing) an existing variable is just = ;

Specifying a type and a name is a declaration - creating a new separate variable.

So change those lines to :

      Extending = false;

I also note a problem in your motor control routines:

void actuatorExtend(){
      digitalWrite(relay1, HIGH);
      digitalWrite(relay2, LOW);
}
void actuatorRetract(){
      digitalWrite(relay1, LOW);   // turn on one relay before
      digitalWrite(relay2, HIGH);  // turning off the other!!
}
void actuatorStop() {
    digitalWrite(relay2, HIGH);
  digitalWrite(relay1, HIGH);
}

You say the relays are active low - one drives forward, the other backward - thus
its presumably an error (short circuit?) if both are driven LOW.

So you always need to set one pin HIGH before the other goes low:

void actuatorRetract(){
      digitalWrite(relay2, HIGH);  // turn off before
      digitalWrite(relay1, LOW);   // turning on
}

You also may have the issue that both relays are on at power-up before the Arduino
gets going. If this does cause a hardware issue you should add physical pull-up
resistors to both relay inputs if they don't already have them.