“It is finished” is Jesus speaking in the past tense to your past, present and future problems.
There is no problem you have been through, that you are going through and will go through that is not captured in that statement, including your mistakes.

“It is finished” is Jesus speaking to the demonic operations in your life.
There is no plot against your life in the past, present and future, including lawful captivity, that is not captured in that sentence.

“It is finished” is Jesus speaking to your sins.
There is no sin – past, present or future – that Christ has not paid for, including the sins of atheists. Once you sincerely repent and believe in Christ, your sins are forgiven, and the power of sin over you is broken.