The practice of giving up something for Lent (e.g., chocolate, meat, TV, the Internet, etc.) is a voluntary private devotion that the Church does not regulate. You are free to set aside that devotion at any time. No sin is committed by breaking such Lenten resolutions. All that is binding upon the consciences of Catholics are the fast and abstinence guidelines of the Church (no meat on Lenten Fridays; fasting and abstinence from meat on Ash Wednesday and Good Friday).
