OK, my first question would be ... how long ago did you know about this AIDS ride, and if it was for some time, why did you only start seriously training for it on May 9th? Why didn't you start earlier??? I'd be nervous too if I was about to do a long ride and had hardly even sat on a bicycle until less than a month before the event.
However, you can salvage things and if you've got enough mental determination, you should be able to do the ride. For you, I think it will come down to mental determination more than physical strength ... being able to continue even when times get tough out there. Remember, you are doing this for a good cause. You've got the sponsors already, you can't let them down, or the people you are trying to help down. Keep that in mind when you hurt, and are slogging through rain and wind out there.
Now on to the physical part:
You need to ride more. Last week was a good intro week, this coming week add an extra 2-3 miles to each of your week-day rides, and do about a 40 mile ride on Saturday. The following week, add an extra 2-3 miles to each of your week-day rides, and do about a 60 mile ride on Saturday.
-- Drink one 750 ml bottle of water and/or sports drink every 1 to 1.5 hours while you are riding.
-- Consume about 250 calories per hour while you are riding.
-- Don't forget to take in some sodium and potassium now and then as well. Dried apricots are especially high in potassium (and area easy to carry and eat on the bicycle), bananas aren't bad. Potato chips and french fries also have potassium, and if they are salted, they've got sodium as well. Salted almonds also have both. (Energy bars will have both as well, but I can only handle those for a short period of time out there, and sometimes I need the extra boost a small bag of potato chips gives me)
You don't have a lot of time to work out equipment issues, but after your 40 mile ride this coming weekend, if you are sore anywhere, make some adjustments and see how you feel during the week. You may discover that a slightly different setup is more comfortable for longer distances. Or that you are struggling to get the energy bars out of your jersey pocket, so you might think about a bento bag.
Have a look over this site for more tips:
Oh yes ... don't forget to have fun! Talk to people while you are riding, take photos, relax!!