When you apologize for a big mistake, consider not asking for forgiveness.
The person you are apologizing to is under no obligation to forgive you. When you ask for their forgiveness you are forcing them to make a decision whether to forgive you. That’s not a fair question and it takes away from your apology.
The purpose of your apology is not to lift your burden. It is to acknowledge that you were wrong and to express your regret for what you did.