Which distance are you riding?
I'm doing the 50 km alone (well i'm in the RMIT team but i don't know anyone) - I always ride with my ipod when i'm solo, but when i do the ATB i will not have an ipod, hopefully i'll be talking to the person next to me..
I'm guessing there will be heaps of people who will be riding at your pace, and it aint like your racing, just go at your pace and enjoy the ride, riding with other always makes you ride a bit quicker anyway!!
You won't get bored, all of those cyclists around will give you all the positive energy, you won't regret doing it, and i'm sure you meet a lot of people on the ride! Might even meet me