What are the implications of "Al Chataso asher Chata"?
Kerisos, 9a: It implies that a man who is intimate five times with one Shifchah Charufah in one He'elam (without remembering in between) is Chayav only one Asham.
Why does the Pasuk repeat "me'Chataso asher Chata"?
Rashi (citing Kerisus, 9): To teach us that the adulterer is Chayav a Korban Asham even if he sinned on purpose.
In spite of the fact that the Torah uses the word 'Chatas" (which implies Shogeg) and that a Korban on a sin generally comes for a Shogeg. See Sifsei Chachamim.