If you've just been at it a month, I'd suggest putting a bunch more miles in before trying the 200k. That'll help you on speed, on navigating, on being comfortable on the bike, on getting used to riding in heat and in rain and in cold and in the dark and in the wind. If you're riding the same speed as some other people, long rides are a LOT more fun. If you're at your physical limits on a ride, that can sort of suck all the fun out of it, too.