Must the Maghrib prayer be repeated if the worshiper mistakenly uttered "My Lord, forgive me" between the two prostrations in the first rak'ah, and completed the prayer without performing the prostration of forgetfulness, and must the subsequent prayers be made up in order?

The cure for obsessive thoughts is to ignore them and completely disregard them. And a mistake in saying "Astaghfirullah" (I seek forgiveness from Allah) between the two prostrations does not invalidate the prayer, for this seeking of forgiveness is a sunnah according to the majority of scholars. As for one who has missed prayers, they must be made up exactly as they were, and it is recommended to observe the proper sequence in making them up.