DNF- the 10k that was a 5k

I woke up at 5:30am this morning, ready to run a 10k!
At 6am I decided to check my iPhone to see who has emailed me throughout the night. (From my west coast family or friends), and there it was, an update from Lawyers Have a Heart race director, "10k changed to 5k due to heat advisory" Ughe. I wasn't prepared for a 5k! I had made my game plan earlier this week, and re-played it in my head over and over throughout the week...for a 10k!
My game plan: Start slow 8 min pace, at the 3 mile turn around, drop my pace to end fast. (~7:30's) which would easily have gotten my a PR, of around 46-47 minutes. (My current 10k PR in 49:11)
I hate not feeling prepared for a race, and this last minute change bothered my running OCD personality! I was so not prepared to run a 5k today.
After some thinking, going back and forth- "Yes, I'll run", "No, I'll just do do the long run", "Oh, maybe I'll do the 4 mile race tonight"...I decided I would go run the 5k, but just as a tempo. That's a fine plan, right? I figured, at this point I will just get my miles in for the day-warm up 1 mile, tempo 3 miles and cool down 2-3 miles. Great plan right? Well, my new plan didn't really go, well, as planned....
"Race" report:
1. At the start, my shoe untied! What the?! I had to pull over to tie my shoe just after crossing the start, and I guess out of habit I turned my garmin off, ughe!(I stop running = I turn off Garmin) Already a bad start!
2. Okay, LLH had wave starts. Wave 1 was for 8 minute mile pace, or less. There were several joggers in wave one. Once I pulled back onto the street to run, post shoe tying, I then was weaving through slow runners. As I went to look at my Garmin for my pace, that's when I realized it was OFF!! (Why didn't I just quit then?)
It just erks me, slower joggers start at the front, it's just rude.
3. Okay, regrouped, shoe tied, and out of the crowds (just after running up the ramp, and turning left to head to canal road) I turned my watch back on, to at least watch my pace, I cruised the first mile at 7:40, and felt fine. I thought maybe I could savage such a bad start, and honestly, at this point my body was feeling great!
4. At the mile and a half turn around, I then decided to start to drop my pace down to 7:30; still I felt okay. I maintained that pace for a little while, and decided I felt good enough still to drop it a bit more. (Figuring I probably only had a mile left to this run) Just after the water stop (I did not see a mile 2 marker, and my garmin was obviously way off) before turning back onto the over pass, I dropped to a 7:17 pace.
5. I was able to hold the 7:17ish pace, until about half way through the over pass; at which time my body decided to start to protest. The sun was blaring, the over pass omitting heat, my legs started to feel weak, and I couldn't get good breath in; I began to worry, and so I stopped.
6. I caught my breath, walk a few seconds and said "F*ck it" to myself, At that point I decided to DNF this run, and I did. I began to start running back in, slowed my pace to 8:30 and jogged in. I did not cross the finish, and did not take a finishers medal.
7. I was able to meet up with a few CAR runners post race, and we ran a nice 3 mile cool down. (The Capital Crescent Trail was nice and cool with all that shade!) I still managed to get my miles in for today: 7. :)
This is my first DNF in years!! I hate the feeling of DNF, BUT it's still so early in the season, I have many races still ahead of me. I'm trying not to feel disappointed or worried about my training-I keep reminding myself- I've been strong at track and tempo, and what really counts is Oct. 9th, 2011!!
One side note: My mental endurance sucks, still. How does one work on that to improve it?
Thanks for reading! :)