Sounds like you have the thought stuck in your head, it can help to complete a thought record (I would recommend this 7 column one from get.gg get.gg/free-downloads-alphabetical-list-of-cbt-wo… ). Doing something like this a few times can weaken the thought by addressing the emotion behind it and the lack of evidence for this on an ongoing basis. If the emotion is shame or guilt say, by finding evidence of times where you were very competent and confident can weaken those feelings by showing this as a one off.