Relax, take a deep breath and thank God that you have turned to Him for forgiveness. Because He doesn't forgive the way we do (we forgive but not forget)but covers us with the righteousness of Christ. If you asked for forgiveness, you need not worry about God punishing you. Yes, you will always live with the pain of knowing what you did, but God will give you that joy that defies all understanding and it will carry you through. Been there, done that, praise God!
Sometimes we find enlightenment through pain. Though I would counsel never to consciously seek it at such a price, especially when the life of another is involved.
Thank you for your kind words.