Please, if Christ is the only mediator, then why do Christians of all backgrounds ask their brothers and sisters to pray for them? Are you aware that’s what Catholics do when we pray to Mary? There’s one Mediator, but there are many mediators, and you yourself have probably acted as a mediator when someone close to you has asked for prayers.
Why confess to a priest? Perhaps you should start a thread on this topic, but in short, Jesus gave power to forgive sins even to men. What good is this power if it died with the apostles?