does it show any deeper than 6'? you might see if there is a software update first... then if nothing changes... try to find someone with the same plugs, and plug your head unit into thier plugs.. that will isolate the transducer to see if that is the problem.

hopefully you didnt trap any air under the transducer when you epoxied it into the hull. air will skew the readings very badly. you have to push the ducer down at a 45 degree angle and slowly roll it into the epoxy to push the air out from under it.  i just did one in my boat yesterday and it is now ready to go. even with it out of the water, it reads 1.8'.

the reason i mentioned a software update, is some of the 700 series were having shallow water issues, and the latest update supposedly fixed that issue.