it appears you previously entered a plea to the crime. This puts you in an incredibly difficult situation. You need to find good new evidence showing that you did not commit the crime. Ask a defense attorney to file a 35(c) motion.
If you have been convicted of being a sex offender, you can not get off the list other than overturning the conviction on appeal. It sound like the time has passed for that. I am sorry
The information provided in this answer does not create an attorney-client relationship. If you are interested in his legal services, feel free to call Chris at (303) 409-7635 at his law office in the Denver Tech Center. All initial consultations are free of charge.
The time to prove you were not guilty was at trial and it sounds as though that is long past. There is a time period and many other factors in determing whether or not you can de-register, such as what type of crime you plead guilty to; a felony or misdemeanor; whether you have ever failed to register before. You sould contact an attorney to speak about your options.