Lakemaster ProMap (in)accuracy

I recently placed a brand new Lakemaster ProMap card into my Lowrance ifinder Hunt C.
To further familiarize myself with the numerous functions and features, I installed a ram mount in my vehicle with the intension of using it day-in and day-out, while on the road.
Yesterday, my travels took me down I35 to Owatonna, back up I35 and I94 to Rogers, back accross I94 and I694/I494 to Woodbury, then back into St. Paul. I traveled through many towns and cities along the way, thus navigating several interstates, state highways, county roads and city streets throughout the day. Overall, about 350 mile traveled, yesterday alone.
The LM card and/or Lowrance-ifinder VERY rarely showed me traveling on the roadways depicted on the map. In fact, I was often times 50-80 feet off of the roadway during my travels!
I’m obviously planning to rely on this unit for semi-accurate navigation during hunting and fishing outings.
If this unit can’t even be counted on to properly display road locations (or my current location) with some accuracy, how can I count on the lake features and contours?
I understand that GPS units are not accurate to within 2″ and should not be used as a primary navigational tool, blah, blah, blah…
What gives?
Do I need to perform a special set-up or calibration to remedy these inaccuracies?
Thanks
cheers