Why is my emt 1/2" conduit offset bend off?
So, why is it when I bend it, that it is 4" instead of 3"?


If your marks are accurate you are apparently overbending the angle. The shrink is not important with EMT since it can easily be cut to fit. Try making two marks 6" apart and see if you can accomplish a 3" offset with the bender standing up. See below.


  Also, even when I used a 2"inch offset with 22.5 angle -- Klein table calculation it is off again by 1". What am I doing wrong? I'm not going past the line?


You should bend offsets on ½" EMT in the standing position holding the conduit in one hand and the bender in the other. Bend the conduit down until the BOTTOM (not the top) of the conduit is even with the angle mark on the bender.


  Also, is their a tool snap collar to measure 180 degrees so I can be exact instead of eye sight when I reverse it the opposite way on mark B? 


Yes, it is called a No-dog or an Anti-dog. But it will not work with a hand bender in the standing position. We just use our eye and sight down the conduit until it looks straight.


  I also noticed that if it isn't exactly 180 on point B it also causes the offset to not be flush with the ground.


This is called a dog-leg and can be remedied in ½" conduit fairly easily by inserting the conduit back into the bender and bending slightly perpendicular to the last bend. Larger conduit is done with a mechanical bender and that is when the No-dog comes in handy since with larger conduit it is very hard to fix a dog-leg.

I would recommend you get a copy of either the Benfield Conduit Bending Manual or Richard Cox's - Electricians Guide To Conduit Bending.

Good luck!