Following the guideline here clearly shows that the action of checking off an item should not be confirmed or acknowledged, i.e. Exactly what the app is currently doing. Please don't change it (at least on Android)
What I would recommend is that the most recently checked off item(s) appear at the top of the "checked off" list, to make it easy to undo.
https://developer.android.com/design/patterns/confirming-acknowledging.html
Following the guideline here clearly shows that the action of checking off an item should not be confirmed or acknowledged, i.e. Exactly what the app is currently doing. Please don't change it (at least on Android)
What I would recommend is that the most recently checked off item(s) appear at the top of the "checked off" list, to make it easy to undo.