Christian perfection is the interior freedom to serve God completely and faithfully at every moment and in each circumstance. Therefore you must look at anything that distracts from or hinders this freedom as the work of the devil. Do I sound too serious? A religious, by public vows, has made their striving for Christian perfection a public property. Thus, any sin you commit, even if it be interior or secret, is a betrayal not only of God and your best self, but of everyone else too.
Penance: to offer a rosary in reparation for my sins.
(My long-standing (14 or 15 years) penance record still holds: to say 15 Our Fathers and then to pray Evening Prayer 'with great devotion')