You can edit your comments, using one of the buttons in lower right corner of the comment. The edit button appears only at your comments (for obvious reasons) and it looks like a pencil.

I know that, and I normally don't have any problems with editing. I still don't know what went wrong with that comment.

I posted my explanation because I had a bet with myself that at least one person reading didn't know how to force a new line, and would like to.

The information for that is under Markdown syntax, an link which is cleverly concealed under the more help link in the help info under each comment.

This is progress, actually, compared to the days when it seemed as though LW had an unnamed and unexplorable mark-up system.