Most rides have shorter options, generally something like a 32 mile route. I would advise scaling back your goal for this ride and shoot for your first metric century later in the season after you have had more time to train for it. Two weeks is not long enough to increase your mileage from 27 to 63 unless you just want to have a sufferfest that day and be miserable. 32 miles would still be a challenge, but do-able.
There is supposed to be a certain amount of enjoyment to biking, and it sounds like this has turned into a very stressful situation for you. There is no shame in saying, sorry, the metric century just didn't work out for me this time, but I am really looking forward to riding the 32 mile route that day!
Grits
2010 Trek 5.2 Madone WSD, SI Diva Gel Flow
2002 Terry Classic, Terry Liberator