Don't sweat things, seriously.
Had my first IM 70.3 in May. Did 2 Sprints last year then in November the Rev3 70.3 with swim cancelled and a MAJOR bike crash and one other shortened 70.3 in March. Went into the IM 70.3 also undertrained and not in too good of a physical condition but the event was so well handled that all nerves disappeared.
Just go with the flow in the swim, enjoy the bike and the run will be so well supported it should be a smorgasbord of food and drinks to keep you going. I took things slow and had a BLAST.