Hi there,
I too have struggled with this scary thought in the past. On the obsessive thinking tape with the program (at least the version I have), Lucinda and the participants talk about having this same scary thought. It's not reality. You need to tell yourself that this thought is just another symptom of anxiety. Demons are NOT going to live inside of you, you love God and they would have no place in your life.
Speak these scripture verses out loud to yourself when you have that scary thought:
"What, then, shall we say in response to this? If God is for us, who can be against us? He who did not spare his own Son, but gave him up for us all—how will he not also, along with him, graciously give us all things? Who will bring any charge against those whom God has chosen? It is God who justifies. Who is he that condemns? Christ Jesus, who died —more than that, who was raised to life —is at the right hand of God and is also interceding for us. Who shall separate us from the love of Christ? Shall trouble or hardship or persecution or famine or nakedness or danger or sword? . . . No,
in all these things we are more than conquerors through him who loved us. For I am convinced that neither death nor life,
neither angels nor demons, neither the present nor the future,
nor any powers, neither height nor depth, nor anything else in all creation, will be able to separate us from the love of God that is in Christ Jesus our Lord." Romans 8 (read the whole passage, really uplifting!).
God's got you! Lay this scary thought at His feet, and focus on whatever task He has for you to do this day. You are safe!
Praying for you!