As a new Christian you still need to work on doing better. The mercy of God isn’t a license to sin and get away with it. That’s the wrong way to look at it. Rather, it’s a grace of God to be forgiven. You need to be contrite, which is to say that you are genuinely regretful. You should understand your failing and have regret – remorse. Humans are messy, and Christians are a work-in-progress. Perfection is sort of an asymptote where growth in the various virtues, in their study and living out your life in their pursuit, increases your perfection.
Part of doing better is “coming clean” if you can: returning something stolen, correcting a lie you told, or admitting a fault.
Proverbs 27:17
New International Version: As iron sharpens iron, so one person sharpens another.
Amplified Bible: As iron sharpens iron, So one man sharpens [and influences] another [through discussion].
This refers to confessing faults and failings to one’s friends to help them not make the same mistake. It’s therapeutic as well.
In Catholicism, a sinner confesses their sin(s) to a priest, and this can also be therapeutic. It’s also a form of accountability. With contrition from the penitent person, the priest prays a prayer of absolution to “formalize” the forgiveness. The priest in this case is standing in for Jesus, as an Apostle. In John 20:23, Jesus granted Apostles the power to on His behalf, forgive sins. According to Catholic doctrine the priest also may assign a penance, which is a prayer or a deed of some sort to compensate for the sin in some way to eliminate punishment in the afterlife in a purification realm called Purgatory, before a saved person can proceed in through Heaven’s gates.
Being right with God is what the Human race is for.
Another part of doing better is prevention. If you did wrong, don’t put yourself in the same position to fail like that again. The Bible talks about a stumbling block – something you trip on that causes you to fall. We are warned to not trip, and to wisely remove that which we trip upon so that it doesn’t happen again. Sometimes our conscience is at odds with our hormones, or our emotions, or our temper, and we have to practice wisdom to avoid a situation that could have regretful consequences.
Another aspect of getting your tendency to sin under control is to spend time in thought. If you find it helpful, write about it privately in a journal. It could just be a Word document or a text file – an opportunity to think concretely if you can hash it out in sentence form by yourself. But also seek help from a minister if you want. Two heads are better than one. You may not want to pay to go to counseling by a psychologist, but a Church Retreat can also be similarly therapeutic, and also in a similarly private setting. The men and women who have gone through church retreats can also be a great source of wisdom in being able to recount how they solved their life crises, and overcame problems and tendencies.
Reference the Examination of Conscience on the Resources page for a questionnaire to help a person walk through what sins they might have committed. Some just pertain to the Catholic faith, but it’s still a good resource for any Christian to consider as one works out their failings of character to become better. God will forgive, however we need to not fail every time we’re tested, and we are liable to be tested – even through situations that seem unfair. So it’s on us to be smarter and be conscientious, and work at it.