Running a Half Marathon

I am running a half marathon this Sunday. Running is the wrong word. I will be power walking because my one foot has a fallen arch. I have never power walked through a half marathon and I feel a certain amount of dread. My normal pace is a 12 min mile. I won’t call myself slow but now I am expecting to be 15 min/mile and I am afraid they will close the course before I finish. I keep telling myself 3 1/2 hours which is the cut off will be enough. But I have this image of myself coming in among the last 5 – 8 people.

Unintentional model:
C – I am signed up for a half marathon on Sunday
T – No one will be there to cheer me on
I am going to be so slow
F – Dread, embarrassment
A – I follow my training plan, put inserts in my running shoes
R – I am dreading being amongst the last runners

I am trying to coach myself to be proud of myself that I am doing this fallen arch and all. Any tips?