I don't know about Calibre, but usual behavior of regexp libraries in multiline mode is to match ^ at the very beginning of the whole string
rather than a line
. Same with $. In multiline mode, you should search for something like:
\nOrder your copy...\n
And be particularly careful with matching a dot (.), as it will match anything including newlines. Code such as .+ will match the whole document. If you really need to use the dot, and frankyly I would recommend trying something like [^\r\n] instead, at least use the ungreedy versions of + and *: +?, *?