There is the Sacrament of Reconciliation that a Catholic priest acting for God can forgive sins if one is truly sorry.
I believe your religion teaches that your priests actually become God, to forgive your sins...Isn't that correct???
God promises to forgive us our sin if we confess them.
1 John 1:9 If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
No need to *prove* how sorry for them you are.
That's just a show for men. God already knows.
And the best way to show that you've repented is to stop doing the sin, not pray a bunch of Hail Mary's and take a trip or two around the rosary.