Turning EV3 precisely has been a problem. Do you use a certain mat for running EV3 on? Can you tell me what material I need to get the mat printed?
Mats are sometimes used with Mindstorms to create line following bots or for defining more complex tasks.
I can't give great advice on printing a mat for EV3, as I've never done this, but I would imagine that you'd want to be able to print on a large, fairly stiff piece of paper or cardboard. If you're just trying to create a basic line for your robot to follow, you can use a piece of posterboard and then add a line with black tape, markers, paint, etc.
There are several different mats that LEGO has made available for Mindstorms over the years:
I believe the most recent is actually the box sleeve in the EV3 kit:
You might want to just purchase one of the officially released mats.