When is this ride? You have some training to do. You should be able to ride 50 miles and feel good after the ride before you do 90. Find Machka on the forums and see her website (or many others) about a training schedule for riding that far. If you have only been bikng a month this is a bad decision to ride 90 miles. It may be possible, but there are so many things to learn about............. you need some more miles first.
If this ride is hot and hilly,you probably will not make it. Wait until next year and ride a lot this year.