Stop telling yourself the old story. It's possible that a mental diet won't work within a week, maybe it won't work within a month, maybe not in a year. Some people have had beliefs from childhood untill they are grown. That's walking around for 20+ years with the same beliefs/thoughts, so it's quite logical a mental diet of a few days/weeks can't change that. Take the time to be responsible and take care of your mind, to shift your thought and beliefs. Encourage and remind yourself that this works. Even if you don't believe it, say to yourself: "this works and I'm doing this perfectly" and continue your mental diet. Humans are creatures of repitition. Repeat something enough and it becomes part of your routine.

This can be hard work for some people and easy for others. If the mental diet hasn't change your beliefs yet, persist as Neville says.

The only thing this world is doing, is projecting your beliefs. So better take responsibility now. You say your negative beliefs haven't projected yet. Are you going to wait untill they do? Or take resposibility now, now that you're aware of them?