My suggestions for your first century:

Don't worry about your time. The goal is to finish it.

Take a break more often than you think you need. I like to stop at least once every 1.5 - 2.0 hours, just to straighten the back & eat something.

Stay hydrated!!

No riding for the couple of days before. This is your time to rest and get your legs ready.

The adrenaline will carry you further than you think.

Have fun!!

Kim