Brennan Manning does a good job of describing the impostor in his book Abba’s Child:
“Impostors are preoccupied with acceptance and approval. Because of their suffocating need to please others, they cannot say no with the same confidence with which they say yes. And so they overextend themselves in people, projects, and causes, motivated not by personal commitment but by the fear of not living up to others’ expectations…
Our false self stubbornly blinds each of us to the light and the truth of our own emptiness and hollowness. We cannot acknowledge the darkness within. On the contrary the impostor proclaims his darkness as the most luminous light, varnishing truth and distorting reality. This brings to mind the Apostle John’s words: ‘If we claim to be without sin, we deceive ourselves and the truth is not in us,’ (1John 1:8).”
The first step in detaching from your false self is to recognize reality.
Pray and ask God to reveal where and when you began to put on this mask. Seek the help of a mentor or counselor. Life is too short to live as someone God never intended you to be.