My 3 1/2 year is "sorry" but goes right back to the same behavior?

whenever my son gets into trouble or acts out by hitting and i tell him to go to time out or i take away one of his privelages he says he is sorry and cries hysterically and after i expalin to him his behavior was wrong he calms down but begins to act up again within minutes. is he really understanding the word sorry or just trying to make me happy by saying that? what should i do to get this behavior under control?