1. There is no harm if you inform your department about your marriage performed few months back.
2 But for this do not change the date of marriage at no costs.
3. Do not worry as failure to mention the fact of your marriage to your department would not cause any departmental proceeding to be initiated against you.
4. Even of you now register your marriage under Hindu Marriage Act , the date of your marriage will be reflected the same July, 2017.
Good luck.