I think as stated above some HIT training on your short days would be great. Learn to eat and drink properly and that will also help a lot. Lastly,,,, you might consider trying to ride hard on your 60 mile Saturdays. Plan on not making any stops along the way. And try to ride a high pace the whole ride. Start slow enough that you can do better on your split comming home. Another approach is to ride what ever you think you can sustain for an hour (20mph) and then each Sauturday push your time at the previous pace by 15-20 mins or more if you can.
You can easliy ride 60 with out stopping ,,, and if you ride hard on Saturdays the "event" with breaks will be easy.

Tapper off about 10 days before and maybe the last 5-6 days only ride short easy rides every other day so you will do your event on real fresh legs. We're all different but I take 2,,, maybe 3 days off before I ride centuries or more and don't work to hard the entire week before as I mentioned above.

You'll already do fine so don't worry and go have some fun. If it's not fun then why even do it LOL!!!