Take a look at
this thread for good instructions on setting up your hitch. It is not set up correctly now if you have no tension on the bars when the chains are hooked up.
You may also want to look at
this one which explains how a WD hitch works. I suggest reading at least the first post that contains the diagram and then reading the set up thread I linked above.
Between these two, you should be able to do it yourself and therefor get it right, and learn about your hitch at the same time! :)
Barney