Usually doing business with a friend is problematic.
The price was probably fair, and you were doing him a favor. It was your first freelance job and it looks like a really great price for your friend. You are learning as you go along. You charged what you thought your time was worth. Your friend should appreciate that as well.
If there is not a clause in the contract that it (the CMS) can be licensed to others, you might consider that as well.