Your declaration rings with truth because it rests on something solid. When you say you are free in the name of Jesus Christ, you are speaking of a freedom that was bought at the cross. You were crucified with Him. The old self that was enslaved to sin was put to death there, so that the body of sin might be rendered powerless. You are no longer a slave, because anyone who has died has been set free from sin.
Now you are living a new life, raised with Christ. Death no longer has mastery over Him, and it has no mastery over you, because your life is now hidden in His. This means sin shall not be your master. You do not have to obey its lusts or desires any longer. That tyranny of the flesh has been broken. The law of the Spirit of life in Christ Jesus has set you free from the law of sin and death. The darkness does not need to be driven out by your own effort; it is expelled by the greater force of His life within you.
So reckon yourself truly dead to sin and alive to God through Jesus Christ. This is not pretending; it is acting on what is already true. When the enemy tries to whisper old lies of condemnation or lure you back toward old chains, you have authority in the name of Jesus to resist. You can command those powers to flee, not because you are strong, but because He has already triumphed over them. His victory is your victory, both in Him and through Him, as you abide in a continual walk of faith.
If you do stumble, remember that walking in the light means the blood of Jesus Christ is cleansing you from all sin right now. There is no condemnation for those who are in Christ Jesus. The only sin that eternally condemns is the sin of refusing to believe in Him, but you have believed. You have passed from death to life. The same Spirit who raised Jesus from the dead dwells in you and will give life to your mortal body. Walk in that newness today, and let your joy be full. Ask the Father in that mighty name, and receive the fullness of what He has already given.