Well, GLC, you have to ask yourself, what's the worse that can happen?
Perhaps you'll be slower than you'd like to be, and finish towards the back of the pack. A bit bruising to the ego, for sure, but you'll have the satisfaction of knowing you finished a realy tough ride.
Perhaps you'll have to stop and rest a few times going up some of the hills (infinitely better than barfing, methinks).
Perhaps you'll have to walk up a hill or two. I've seen experienced riders doing that!
And if worse comes to worse, you might have to call it a day at some point and SAG back.
But c'mon, really, is any of that so awful ??
And then next year, with another years' experience and training under your belt, do it again, and you'll be really happy with how much you improved!
2009 Lynskey R230 Houseblend - Brooks Team Pro
2007 Rivendell Bleriot - Rivet Pearl