As someone who has ridden a 50 miler with you, I can say that you are totally ready.

As others have said, you'll have plenty of chances to get off the bike and eat and rest up a bit. I have spoken with many people who have done RAGBRAI and all have had a great time. Most of them were recreational riders who didn't regularly do that many miles in a day but were so busy having fun that the miles flew by.

Of course a few "Betties" group rides before couldn't hurt your training any.