I am currently working on using line trackers so far i have done a good job. But i still cant figure out how to make my robot turn when it confronts a corner, i am thinking of placing the in the middle but i font know if that will change anything, or should use encoders to make turning on sharp corners better,0

In my experience, a triangle configuration has worked well.

For detecting things like corners, you basically want to start checking the status of all three sensors. If you're using three sensors, this gives you 8 unique conditions to check for. For example, if you're looking at a right corner, like this:

_
|
^

You would want an if statement like