Question: I am Developing a wordpress testimonials plugin.

I created a custom post type also display and working proper. But now I want to add more fields like "Company Name", "Websites". I know I can manage from this by adding custom fields, but I want to add a separate section for that. 

Can anyone help me figure out how to do this?

Answer: 
You can also implement meta boxes which will be displayed on the right hand sidebar the same as you have categories displayed.
You can use "Advanced Custom Fields", which is a perfect solution.