Only just seen this thread, Connemmara, and you know what they say, "the person does not exist who has never made a mistake".
I know myself that it is harder to forgive yourself for something than it is to forgive others but I think, if you sit and think of the ways you have made amends for that that mistake in other ways, the better you will feel.
If others have been affected, is it too late to ask for their forgiveness?
God bless you, and whatever you decide, I'm am sure it will be the right decision.
It's hard to keep living with a mistake that could affect the rest of your life.