Alpine brings up a good point. Some people do need to try more for confidence on race day. Physiologically, it's not necessary, but psychologically is an entirely different question.

I've never had an issue with training for distance. I have plenty of confidence going into an IM with my longest training run being only 15 miles, my first marathon in fact, was part of my first Ironman.

So you need to pick out a plan that you think clicks with you. Maybe you need more distance to get your confidence, maybe you're a mom with 2 kids and you need more time. Either way, have fun with it and ask lots of questions.