Just a quick note;
In replying to Secularfirst, I attached a list of factors considered when making a H&C decision. Go over them, and when writing your letter try to show how each of these factors are a positive in your case.
My two cents on writing your H&C letter,
1: Stress you did not choose to leave Canada, stay abroad for as long as you did, and violate your RO.
2: Emphasize that you want to return to Canada permanently, be a productive member of society etc. Stress that now that you are an adult and in charge of your life, you will fulfill your RO and make Canada your home.
3: Be preemptive and say that while you are 22, you only found out now that your are a PR (attach supporting documentation) and that you acted on it as soon as you found out. Also emphasize that had you known sooner, you would have tried to return as soon as possible.
4: Express to the panel what hardship you would suffer if you lost your PR status, how this would affect your life.