if(Serial.available()){
for (i = 0; i < 11; i++){
for(pos = 20; pos <= 120; pos += 1){
myservo.write(pos);
delay(15);
}
for(pos = 120; pos >= 20; pos -= 1){
myservo.write(pos);
delay(15);
}
}
}
Once the serial data arrives, you never bother to read it. Why not.
The if statement is not going to wait for serial data to arrive.