Most of these events can be walked or jogged if you are not a runner. Most people can walk the 5k distance (3.1 miles). The only person you need to beat is yourself. So relax on the pressure, and sign up for this great event, or one near you soon. The atmosphere and camaraderie are contagious.
Lots of these sort of community events support local causes, too.
Most events include a t-shirt in the entry fee! It is fun to collect the t-shirts and see people around town with the same t-shirts you have.
Just get out and do it!