Vicki!
Congrats! I don't think I am the one to give advice since I always come in much closer to the end of the pack. But I agree that the road riding seems to really build your endurance. Our local annual August ride (the Ore to Shore) usually has more than 1000 riders, but it's a real blast and plenty technical for me. So my only "advice" is to continue with the road riding, get real comfy on the trails and have lots of fun!
Nancy