What really is the issue here? The fact that you have a very free form open ended assignment? The fact you stressed out over finding out too late? The fact that he can't/won't make time for you?

Your first step is easy. Pick a personality theory.

Then you either design a therapeutic approach, or apply it to a situation/problem from everyday life.
And then as a third option is comparing the personality theory in as theory vs practice kind of way.

Then you need to show that whatever theoretical concepts the course introduced you learned by using/applying them.

You should also find a way to avoid thinking about quitting when you get stressed out.