Yes, you can't let go of something if you are focused upon it. So focusing on "hatred, anger, worry, jealousy, envy, sorrow, trouble or disappointment of any kind" is just going to perpetuate it.

Focusing instead on positive thoughts (even if barely activated) would be my strategy with this exercise.

See also: Master Key System, Exercise 4: I can’t seem to get certain songs out of my head. Am I doing something wrong?

The exception to this idea is when you focus upon something negative with the explicit intention of deliberately trying to find an ideally-permanent better-feeling way to look at it which doesn't produce negative emotion.

This is basically the idea behind the Manifesting Experiments on this website, especially the second and fourth experiments.

But you only really need to do that if the subject keeps reactivating in your life for some reason, maybe because something in your physical circumstances keeps reminding you of it.

Most of the time you can just turn your attention away from the negative thoughts onto the positive ones and just never look back.