There are quite a few different versions of the Act of Contrition. Below are several that you could use.
The Original & Traditional Version of the Act of Contrition.
O my God, I am heartily sorry for having offended Thee,
and I detest all my sins because of thy just punishments,
but most of all because they offend Thee,
my God, who art all good and deserving of all my love.
I firmly resolve with the help of Thy grace
to sin no more and to avoid the near occasion
of sin. Amen.
Alternative Version
My God,
I am sorry for my sins with all my heart.
In choosing to do wrong
and failing to do good,
I have sinned against you
whom I should love above all things.
I firmly intend, with your help,
to do penance,
to sin no more,
and to avoid whatever leads me to sin.
Our Savior Jesus Christ suffered and died for us.
In his name, my God, have mercy.
(from the Rite of Penance)
Jesus’ Prayer
Lord Jesus, Son of God,
have mercy on me, a sinner.
Act of Contrition Inspired By The Gospels
Lord Jesus, you opened the eyes of the blind, healed the sick, forgave the sinful woman, and after Peter’s denial confirmed him in your love.
Listen to my prayer: forgive all my sins, renew your love in my heart, help me to live in perfect unity with my fellow Christians that I may proclaim your saving power to all the world.
Act of Contrition Inspired by Psalm 51
Lord God, in your goodness have mercy on me: do not look on my sins, but take away all my guilt. Create in me a clean heart and renew within me an upright spirit.