Please let me urge you to sign up for a 5K. Any one, pick one, as it doesn't matter, really, which one it is. The energy, fear, excitement and finally, the achievement will be amazing to you and to your brain. The sheer cumulation of the above emotions will let you finish.
You'll run, then you'll walk for a while, then you'll trot for a little while and walk some more. Then, you'll find someone who inspires you to run even a little longer, then you'll walk and huff-and-puff for a while. Finally, you'll decide that it's time to run so you can at least be running when you cross the finish line--and no, you won't be last. Your cheeks will hurt from smiling. Your eyes will be swollen, holding back tears that only you will know exist. Your inner-parent will pat you on the back and lift you up in the air like you're 5 years old again, having just ridden on two wheels for the first time.
Pick one. I ran my first one with no friends nearby because I didn't want to be embarassed or feel like I was holding them up--they ran way ahead. I prefered the solitude with my ipod.
Your next step is to pay the $40, get a free t-shirt. and do it. (I'll pay you back if you hate it).