This is a feeling that deserves to be treated with respect, perhaps it's to the credit of the therapist that you have gotten in touch with it?

Yes, it's unpleasant to feel that way and it may also be that there's something in the relationship with the therapist that exacerbates the problem more than just getting in touch with something left over from childhood? That's what happened with a lot of therapists, for me, and I didn't recognize the therapists' contribution to overly activating things, sometimes making them worse, and not helping to resolve them.

I'm not a clinician and so, obviously, take what I have to say with a grain of salt or completely ignore it, but with regard to this kind of thing I really like Heinz Kohut's theories. Schema therapy also, as I understand it, has ways of trying to identify such feelings, or schemas, and then dealing with or overcoming them.

If you want my inexpert thoughts about the situation, according to what I understand about Kohut, you can send me a PM. His stuff also has some suggestions of ways out, as I recall. No guarantees, of course.

I don't think you're an imposter. Maybe the therapist is an imposter therapist, I don't know? At least sometimes, maybe.