Marijuana use. How confidential is the DODMERB

I am a senior beginning the ROTC scholarship process. As a sophomore, I made the stupid decision to try weed once or twice. I no longer do that anymore and I deeply regret my stupid experimental actions. That being said, I still did it. I have read some places that if you only did it 1 or 2 times its not worth putting it down. Other places say that lying is worse than smoking. Honestly it would eat away at me if I lied so I will 100% tell the truth when the time comes.
One thing I am worried...

Marijuana use. How confidential is the DODMERB