I'm not sure how to a manipulate the positioning and size of a long table on the page.
With a regular table I have tried the
adjustwidthenvironment from chngpage and the
\scaleboxcommand from graphicx, but they don't seem to be compatible with longtable. Trying to change the font size with
\footnotesizealso doesn't seem to work.
Here is a working example of the table: