New to Ironman, not new to Triathlons

I will be doing my first 70.3 in March. I started doing triathlons at age 21. I grew up in San Diego, but I had no idea of the history the sport had here until I stumbled upon it in 2010 with my first sprint. I've always been a runner and I have completed several half-marathons or shorter and 2 full marathons. In the world of triathlon I have finished sprint and international distances. I am in the process of training for my longest tri to date, the Half-Ironman. Though I am not new to this sport per-say, coming into this new distance makes me feel inexperienced.