I am a young Muslim female (19), I am Islamic married but I have not told my parents or any of my family but there some such as my cousin sisters. All of my husband side of family know that we got married but my family don't not know. I want to ask have a done something wrong? Have made a sin?
Being a young lady you sure need the permission/blessings of your parents or elders and also needed a "wali" who could have given you in marriage to the gentleman you are married to. It is noteworthy for all Muslims to understand that these are basic requirements of a valid "Nikah" Unless there are some legitimate reasons (permissible in Sharia'a). You failed to mention the reason for hiding your marriage from your parents or family. Which creates doubts that, most probably, you know the requirements but something wrong made you hide it, circumvent it.
Muster courage, address the wrong and seek the permission and blessings of your parents and then consult some learned scholar to see how you may extricate yourself out of this sinfulness; which you have been in; since you supposedly got married; and continuing in till now, by paying "kaffarah". Maybe, that you have to get out of this marriage altogether or do the "Nikah" again. (depending on the real-time factual circumstances, you were in at the time of marriage). Although I am not trying to scare you and wish you the best of luck, You should be mentally ready for all eventualities.