Zundra, you should report it anyway. I know it’s tough and scary, but it’s your obligation as a citizen and as a Christian to do so. The police and Child Protective Services receive tons of these reports annually. They’re very familiar with the process and the emotions involved. I used to work at a child advocacy center. The abuser will always deny doing anything wrong, that’s nothing new. The victim will also often deny that anything bad happened. This occurs when she considers herself old or mature enough to consent to sex or if she feels that her abuser really loves her. The police know this. But an objective third party randomly making a serious accusations with no reason to lie? Very rare. You will be taken seriously, Zundra. An investigation can uncover the truth. And even if this girl never gets justice, that fact that you reported it could help protect someone else from him in the future. For example, should he start abusing someone new and the new victim did want to press chanrges, your documented report demonstrates to the police and to the court that this has been a problem in the past and the new victim should be taken seriously.
As for confession, if you were praying that this man be paralyzed or hit by a bus or something similar, you should confess it. We’re to pray for our enemies’ wellbeing and conversion of heart, not that they be smited. If your were instead praying for the safety of the girl involved and asked for “something severe” like a prison sentence to prevent him from harming her again, then I wouldn’t consider this a sin. But either way I would suggest you go to confession and explain the situation to a priest. He has heard everything before. He’s heard people confess child abuse, praying for someone else’s demise, anger, fear, everything. Nothing will shock him.