The analyses of a text #7

The protagonist recalls his childhood.
He and Peggotty, the only maid of his house came to Yarmouth, her hometown and visited her brother, Mr. Peggotty's house.
Em'ly is Mr. Peggotty's cousin, whose father was drown-dead.

She started from my side, and ran along a jagged timber which protruded from the place we stood upon, and overhung the deep water at some height without the least defence. The incident is so impressed on my remembrance that, if I were a draughtsman, I could draw its form here, I dare say, accurately as it was that day, and little Em'ly springing forward to her destruction (as it appeared to me), with a look that I have never forgotten, directed far out to sea.
The light, bold, fluttering little figure turned and came back safe to me, and I soon laughed at my fears, and at the cry I had uttered, fruitlessly in any case, for there was no one near. But there have been timessince, in my man hood, many times there have been, when I have thought?Is it possible, among the possibilities of hidden things, that in the sudden rashness of the child and her wild look so far off, there was any merciful attraction of her into danger, any tempting her towards him permitted on the part of her dead father, that her life might have a chance of ending that day. There has been a time since when I have wondered whether, if the life before her could have been revealed to me at a glance, and so revealed as that a child could fully comprehend it, and if her preservation could have depended on motion of my hand, I ought to have held it up to save her. There has been a time since?I do not say it lasted long, but it has been?when I have asked myself the question, would it have been better for little Em'ly to have had the waters close above her head that morning in my sight, and when I have answered Yes, it would have been.
This may be premature. I have set it down too soon, perhaps. But let it stand.
[David Copperfield by Charles Dickens]
I'd like to know this means "her death."
I'd like to know what "set it down" means here.
And I'd like to know what "let it stand" means here.
Thank you in advance for your help.