Yes you can. But expect to have a real fight on your hands.
If you’ve already confessed to a crime but now wish to plead not guilty in court, then you’re free to do so. You should know however that these cases are brutal court battles. Don’t automatically expect the free attorney you get in the JAG Corps to be up to the task of winning a “confession” case. He or she will likely tell you to just plead guilty and get it over with.
The Bilecki & Tipon team can and will fight for you if you’ve confessed. But you need to acknowledge the difficulty of your case. Hiring a relentless defense team is your only real option at this point.