We are not too concerned about the specifics of your meditation technique, only that you are sitting with your eyes closed, back straight, hands on your thighs, continuously reminding yourself that you are observing everything that is happening in your experience.
We really suggest doing two 20 minute sessions, because 40 minutes in a row can be very grueling at first.
Just find a pillow or chair, sit on it, set your phone alarm for 21 minutes so you have a minute to get comfortable, and go. Just observe what is happening in your inner world.