Urgent question to Christians about repentance and restitution?

A few years back I used to lie on my time sheet at work and put more hours than I actually worked and so i got paid more money than I earned. Now that I have repented and given my life to Christ (though still struggling a bit with leaving sin completely), I want to return the money I wrongfully took. I have estimated that I was paid 500$ that I did not deserve during my time at the job. I have the money but I was wondering if it is still considered restitution if I write an anonymous letter apologizing for what I did and sticking the money and the note in an envelope and dropping it off at the payroll office? Or do I actually have to confess face to face before God counts it as restitution? I really want to do what's right but I don't want to get into legal trobles :-( Please advice