If so, is it best to be rid of it? My whole experinece of life has been re-evaluating miss-steps and mistakes

I am very sorry to hear about your experience of ife so far.

Generally, when plagued with the idea that one is 'possessed' by a false self or persona, its best to address this in the setting of our own daily life. Increase wholesome social connections, spend more time with family and friends who are supportive of such a problem. If such a belief becomes very strong and associated with such a belief is the inability to maintain social relationships or keep a job, conventional stuff, then its best so seek the assistance of a qualified therapist/psychologist/psychiatrist.

Meditation practice done with a certain momentum leads to the experience, knowledge and wisdom of how the sense fo self is a 'construct' coming into being in response to circumstances and experiences which in turn are also 'constructs'. So for a period of time a meditation practitioner may form strange views regarding the self. But the context being meditation practice, that itself provides the necessary feedback to the practitioner that any view regarding the self - It exists, it doesnt exist, its true, its false etc etc is simply a 'view'. A meditation practitioner is thus equipped to deal with such views knowing that all views are constructed, all views are unreliable, all views do not represent the self, do not own the self and are in turn not owned by the self. Thus meditation practitioners through their practice over a period of time learn that it is in fact impossible to be possessed by a self (true or false) and in turn it is impossible to possess that self.

It's actually better to accept it and "develop" it further. The trick is to use the negative feeling as fuel for making positive developments in your life. When you are on a good path, then miss-steps and mistakes aren't a big deal, it's just part of the process.

Everytime I worry about my imperfections, I try to remind myself "the life of a zen master is one mistake after another"

You might like this: The Practice of One Continuous Mistake — Monterey Bay Zen Center 

Best wishes Berna!

I can relate. Most days I feel defeated. I've hungered for an exorcism before. But as far as I can tell, the way forward is self-acceptance, not self-rejection. Patient love, not internal fascism. Wait for the prodigal son to return. A surrender to what arises, a courageous acceptance, even if it's horrible, even if it's failure, even if it's negligence.

What that means in terms of specific technique depends on where you are in the path. But it boils down to surrendering to what's already here. For a beginner, that could look like a noting practice, instead of trying to force and strain your way into a different life. For someone more advanced, it's resting in stillness, resting in action, resting in everything. Giving away all control and influence. Nurturing a soothing, lovely trust in all that arises. Letting effort and care arise on their own. 

All mental phenomena, all behavior, is not you. You didn't create it, you don't manage it, and you can't influence it one bit. Realizing this fully may bring you relief. And it can help to try to question your fears, question your anger — are their threats really true? Is this narrative of failure really true? Putting down the stories, even just for a moment, can feel great. 

No, it's not possible.

False selves and persona's aren't entities, and possession would be that of an entity possessing another entity. Laid bare, false selves and persona's are beliefs. 

Miss-steps and mistakes are also beliefs. They'd subjective judgements. Just opinions. 

That there even are miss-steps and mistakes isn't objectively true. Just judgements. Opinion.