Hi, My name is Philip. I am an attorney with over 16 years experience. Hopefully I can help you with your legal question.
I would "fall on my sword" at this point.
The fact they do not have a sworn statement is not really significant. You told the 1SG...that would be admissible (if this landed in court). So I do not believe at this point it would be a good idea to "turn around and deny the confession"
The fact you "came clean" and the fact you have a spotless record? That is significant. I would expect that to help you out quite a bit. It may be they still impose punishment, but I would expect the punishment to be reduced based on your record
In the officer
corps (for all services) there is an expectation that if an officer screws up, they take full responsibility. The term "fall on your sword" dates back many years and means, basically, for one to admit to and take responsibility for their actions. It seems you are in the middle of this now...no good reason to turn around.
I would go into Art 15 and admit guilt. Then I would explain the plan you have to make sure this does not happen again. It may be they suspend any punishment...and, it MAY be they will consider vacating the punishment altogether (after a period of time) which would remove the Art 15 from your record.
Please let me know if you have more questions...happy to assist if I can