1. One who erred and when praying the Amidah mentioned something which was not applicable for that day (e.g. he said the Shabbos blessings on a weekday or said Ya’aleh Veyavo on a normal day which was neither the new month nor a festival or if he said Al Hanissim in the middle of the year etc.), does not need to repeat. (Shulchan Aruch, Chida, Ben Ish Chai and Kaf Hachaim). Some say that if he is still in the middle of a blessing that he should return to the beginning of that blessing. Nevertheless, if he has already finished the blessing, he does not repeat (Mishne Berurah 108). If he mentioned something which is not an untruth at all (e.g. by saying Zachreinu Lechaim or Attah Chonantanu, or if he said Ya’aleh veyavo without the words Rosh Hachodesh hazeh), everyone agrees that one does ot repeat.
2. However, if he realizes in the middle that he is saying the wrong thing, he should stop immediately even in the middle of a blessing. (ibid)
