Is a wife sinful for opening the door to someone she thought was her husband, especially after she had doubts due to the time of his arrival?

There is no sin upon you if you did not intentionally commit a forbidden act, such as appearing before a man unveiled. Your husband should not have gotten angry and scolded you; rather, overlooking minor slip-ups is desirable. Apologize to your husband and explain the truth to him: that if you had intended ill, you would not have told him. In the future, do not mention to him anything that serves no beneficial purpose.