Admittedly, I don’t know much about Catholicism, but don’t they just go to confession and say a “Hail Mary” or something and all is good again?
No, you are not correct but thank you for being so kind to Catholics with an honest question! Seriously.
We must not only confess and say the pennance but also be sorry for our sin. This is where many people will fail. Unless they are truly sorry, the confession means nothing.
We must also swear to not sin again. Not that we don’t fall off the wagon, so to say but, for example, if one is living in sin, unmarried and having sexual relations, one cannot just go to confession and continue living that way. A Catholic must turn from sin for the confession to be valid.
Not if they intend to continue doing the same sin. That's called being unrepentant, and no empty or halfhearted words will erase it!!
BTW it's the same throughout all Christianity.