I do that too. All we can do is be aware of it, then realize we don't have to censor. We are 'allowed' to be who we are, fully and completely.

One reason we do that is that we don't want to 'look at' ourselves, admit our motives, write down something that might make us 'look bad'. It is the same kind of censoring that can happen in therapy too.

Like in therapy, journal censoring can get better with practice. You might want to keep it short, or limit the time you write each time. (I find the longer I write the more I want to censor or embellish). You might want to just write down "X" happened and my reaction/response was "Y", to get started.

Or maybe your therapist has some helpful idea ?