You use expressions such as if I'm not mistaken and unless I'm very much mistaken as a polite way of emphasizing the statement you are making, especially when you are confident that it is correct.
双语例句
例： I think Alfred wanted to marry Jennifer, if I am not mistaken.
我想如果我没搞错的话,当时艾尔弗雷德想娶珍妮弗。