What is the ruling on prayer if the one being led in prayer (ma'mum) doubts whether he completed the Fatiha after being distracted by correcting the imam, bearing in mind that reading the Fatiha is not a pillar (rukn) for the one being led in prayer according to the majority of scholars?

Your prayer is valid, and you did the right thing, because doubt after finishing the recitation should not be entertained. We advise you to ignore these whisperings (waswas), and we ask Allah to cure you of them. We also recommend that you persist in supplication and humility, and that you distract yourself from these whisperings. We further advise you to consult a trusted psychiatrist.