Is what a girl does with her husband - after the marriage contract and before the wedding - in terms of getting to know him and showing affection, considered shameful and contrary to social customs, and is her mother's and sister's statement correct that the husband has not yet become her husband?

If a woman's marriage contract with a man is legally concluded, she becomes his wife, and whatever is permissible for a husband with his wife becomes permissible for him with her. Therefore, what you did with your husband is not forbidden. What your mother mentioned about it being shameful might be due to their local customs. You can clarify that Islamic law does not prohibit this. If your mother prevents you from doing something that would cause them embarrassment, then you must obey her if it benefits your parents and does not harm you. However, you must be cautious about discussing sexual intimacy and marital relations between spouses through modern communication channels for fear of others seeing it.