It is a run on sentence, i.e. two sentences improperly joined into one. "Therefore " does not work as a connective.
One solution would be to separate it into its two statements. "I made an error" is the first statement. "I did something about it" is the second statement. Each statement requires its own sentence.
Or you could combine them into a compound sentence using a correct connective such as but. "I made a mistake, but I ..."
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