If the heart wanders or is distracted, bring it back to the point quite gently -- and even if you do nothing during the whole of your prayer but bring your heart back, though it went away every time you brought it back, your time would be very well employed.
God requires us to be oriented from moment to moment to what is in the timeless, and not to be stuck with our thoughts and fantasies of blaming and self-pity and the belief that the past is responsible for our present problems. What is needed is to understand life in the dimension of the timeless, where everything becomes meaningful and self-revealing.