All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we ask Allaah to cure you from this disease a cure that leaves no sickness, and we ask Him to forgive your sins and be pleased with you.
We hope that what happened will be a lesson for you so that you will benefit from it in your worldly and religious matters. You should first take the initiative to repent for trying to sexually assault that girl, and secondly, to repent for lying. For more benefit on the conditions of sincere repentance, please refer to Fataawa 87903, 86527 and 88108.
Therefore, it becomes clear to you that if the sin is between you and another person, you should first seek his/her forgiveness. Hence, you should seek the forgiveness of that girl and her family from what you have done but you should not tell them what you did; rather, you should ask them to forgive you in general. However, if you fear that this will cause a greater harm to you, then after repenting, you should supplicate Allaah for them and seek the Forgiveness of Allaah for them. Also, you should perform good deeds as much as possible and avoid any means that could lead you to committing such a sin or any other sin again.
Allaah Knows best.