Are you putting the J bolt through the flat end or channel end?? There are three holes so your description of "the hole" is a little vague.
The J bolt goes through the outermost hole on the flat end of the mount
If it still wont tighten sufficiently shorten the fixed end of the carrier.
As an additional precaution place a cable around the spare and chassis, its not un-common to get to where your going and find a missing spare...