Bike for upcoming 70.3?

Hoping for some insight here. Looking for a bike for an upcoming 70.3. I am not a serious cycler, it is my weakest link. I’ve been using a hand-me-down Fuji Newest and I hate it. I feel wobbly, out of control, and every little bump feels sketchy. This is probably mostly user error (VERY nervous rider) but I need something more comfortable that can handle thicker tires. I do not want to spend more than 700-800. Yes, I know there are faster bikes but I am not fast. I think I will be faster if I’m a little more confident. Just trying to get through it 😅

Going to look at both of these bikes this week—anything I should be aware of? The Specialized has Shimano 105, the Trek has Sora (I think?) The Specialized says carbon fiber. Should I avoid this from a durability standpoint? Any help is appreciated!!