Idiom Meaning "Ready to Correct One's Mistake"

I'm looking for a concise way to describe this situation:

Person A compliments B's team at a competition. But B does not respond to this compliment gracefully, even though it means a lot to him. B senses that doing this has hurt A, but pride or shyness get in the way of him clearing the air with A about this for a while. When B works up what's needed to talk to A, unforeseen circumstances change B's plans and he loses touch with A. Years pass, but B continues to feel an urge to fix his mistake. B does not actively seek to fix it (aside from learning from it), but if the opportunity to do so presents itself he has told himself to take it.

One idiom I've considered is turning over a new leaf. But this phrase seems better for a personality overhaul than for repairing one mistake.

Is there a word/idiom/phrase (WIP) to describe a person who would leap if given the chance to correct a specific mistake he made?

Edit: I have received some great answers, but I've realized I have one more condition I'm looking for: I'd prefer a casual/conversational WIP. Thanks!


He wants to "atone" for past behavior

Definition of "atone" from Google

Verb

Make amends or reparation: "he was being helpful, to atone for his past mistakes".

Synonyms expiate - redeem

EDIT:

Another idiomatic alternative is "to make amends":

From Merriam-Webster Online Dictionary:

Make amends: compensation for a loss or injury : recompense

Origin of AMENDS

Middle English amendes, from Anglo-French, plural of amende reparation, from amender First Known Use: 14th century

Example - step 8 from the 12 steps in a 12-step program:

8. Make a list of all persons we had harmed, and became willing to make amends to them all.


Not quite sure if this is what you're looking for, but the word "repentant" is the first that comes to mind. Other possibilities for single words might be "contrite", "penitent", "rueful", "compunctious" or simply "regretful". Not really sure about phrases or idioms, though. Hope I've been at least some help!