I agree with Jcleppe, because if you did successfully pass SFT, you would now be contacted no matter what, and believe it or not because of manpower issues, it is rare that this option is offered upon dis-enrollment. The majority of cadets that leave as a 300 or given one option...pay back what you owe us, and goodbye to the service in every manner.
AF has no problem meeting their quotas, hence why the goodbye.
I would have a one on one with your ROTC adviser for guidance regarding why now you want to leave ROTC, but enlist. Is it financial, is it academic, etc.? These issues will be discussed if you want to enlist because your CC will also be part of the dis-enrollment process for AFROTC HQ as a POC.
They need to understand why 2/3rds through you have decided to leave ROTC, but want to stay in the AF. They maybe able to assist if it is academic, or financial through guidance and resources available that you have yet to realize exist.
Good luck.