まぎれじゃありませんでした
紛れじゃありませんでした
magirejārimasendeshita

Noun
Desu Copula

The polite, past negative form of まぐれ

1. It was not a mistake.; It was not an error.; It was not the case.

Past/Perfective
Negative
Polite
Terminal Form
Usually Written in Kana