If your retirement date is set after 1 SEP you will be considered for continuation to 24 on the board happening next week. I was late to rate and took the 20 year, so I am now in a boat where I have to leave even if I don't want to.
If you took money up front, they will recoup it. Depending on how on the ball they are, it may show in your final paycheck. Although I am told it can take 4-5 months for the AF to notice. At that point, they will start by taking back 2/3 of your retirement check for as long as they need to.
You will get your last bonus check, but remember that they pay you for the year you are about to serve, so most of that will go back to them depending on dates and such.
Hope that helps (from a guy living the exact same story. Forced to retire 31 AUG, with 4 years left on ACP.).