Working motor reversal code with a unsteady delay

unsigned long currentMillis;
unsigned long previousMillis;
unsigned long previous2Millis;
const long onInterval = 10000;
const long offInterval = 20000;
const byte in1 = 3;
const byte in2 = 4;
const byte sw1 = 6;  //this is left switch
const byte sw2 = 5;  //this is right switch
boolean sw1Status;
boolean sw2Status;
int stateMachine;

void setup() {
  // put your setup code here, to run once:
  pinMode(in1, OUTPUT);
  pinMode(in2, OUTPUT);
  pinMode(sw1, INPUT);
  pinMode(sw2, INPUT);


}

void loop() {
  // put your main code here, to run repeatedly:
  currentMillis = millis();
  sw1Status = digitalRead(sw1);
  sw2Status = digitalRead(sw2);

 switch (stateMachine) {
    case 0: //motor stop/ reset
    digitalWrite(in1, LOW);
    digitalWrite(in2, LOW);
    if(sw1Status == HIGH && sw2Status == LOW)  //tray is tilted to the left
    {
      stateMachine = 1;
    } else if (sw1Status == LOW && sw2Status == HIGH) {  //try is tilted to the right
      stateMachine = 2;
    }
    break;  //erase the break see what happens

    case 1:  //go right
    if(sw2Status == LOW) {   //go right until the right switch is high
      if(currentMillis - previousMillis >= onInterval) {
        digitalWrite(in1, HIGH);
        digitalWrite(in2, LOW);
        previousMillis = currentMillis;
      } else if (sw2Status == HIGH ) {
        stateMachine = 0;   // go to reset
      }
    } else if (sw2Status == HIGH) {
      stateMachine = 0;  // go to reset
    }
    break;

    case 2:  //go left
    if(sw1Status == LOW) { //go left until it touches left switch
      if(currentMillis - previousMillis >= onInterval) {
        digitalWrite(in1, LOW);   //go right mechanism
        digitalWrite(in2, HIGH);
        previousMillis = currentMillis;
      } else if (sw1Status == HIGH) {  //if it touches left switch
        stateMachine = 0;  //go to reset
      }
    } else if (sw1Status == HIGH) {
      stateMachine = 0;
    }
    break;


  }
  }