First of all, you mentioned in the article that we promised 45 stalls for that day, but you are completely mistaken as we announced only 35.

mistaken 是动词 mistake 的过去分词形式，在句中作形容词使用，表示"错误的、弄错的"。mistake 本身由前缀 mis-（表示"错误"）和 take（拿、取）组成，字面意思是"错误地拿取"，引申为"误解、弄错"的意思。