As others have said, you'll go do 23 miles just fine. Once you do 20+ you'll have a hard time going back to 10
My overall fits and cycling skills jumped dramatically when I went from doing 15-20 mile ride to regular 25-30+ rides.
I wouldn't worry to much about pre race/event stuff other than make sure your bike is ready to go, extra water and snacks for on bike during the ride and a good nights sleep and proper hydration the night before.