My moral misgivings are that I taught her that dad is a sneak who will lawyer-ize stuff out of you by misleading you (even if she's happy with amount of money she has).
What say the moral philosophers of APS? A hundred bucks is a significant sum to me, but chump change compared to my daughter thinking I'm honest and she can trust me.
I'd say anybody who would lie to his daughter is lower on the scale of evolution than a snake. In my straight-arrow world, you cheated your daughter. The operative portion of your entire sorry saga is this:
"I told her I'd give her a hundred bucks if she did it." That statement very clearly implies a contractual
quid pro quo -- Party A double bags rotting carcass, Party B pays $100 as compensation for said double bagging. Weaseling out by telling her
after the fact that you didn't mean you would pay her $100 to bag the carcass, but that you only mean you would pay up on money you already owed her, is pretty low.
I'd say you taught her an important lesson, all right: Always get it in writing, and always read the fine print.
So ... moving on to the "How do I apologize" part -- perhaps pointing out that you had intended to teach her a valuable lesson, and that you realized after the fact (after being soundly thrashed by your so-called friends) that the lesson actually conveyed was the opposite of the one you had intended.