Screwed up programming my Garmin 305--and ended up with a huge PR

I haven't run a decent stand-alone 5k in 8 years, since I ran 20:57 when I was 27 years old.  I ran the same race last night, and decided to use the Virtual Partner on my Garmin 305 for the first time to pace me.  Based on race times in other distances and in tris, I thought I could beat that time by a couple seconds.  I programmed the watch for 3.11 miles in 20:55, thinking that would give me a slight PR and I could maybe pickup a few more seconds in the last 1/2 mile.  On the drive to the race, I wondered what would happen if the race ended up being 3.12 or longer by accident.  Would the watch just stop?  Sure enough, it does.  So I extended the distance to 3.19 just in case, but I forgot to change the time, so unbeknownst to me, the target pace was now 6:33/mile instead of 6:44.  During the race, the only display I glanced at was how many feet in front of or behind my virtual partner I was.  I felt great, and was beating my virtual partner by a couple hundred feet, which is about 20 seconds or so, and I would have been thrilled with the resulting time.  And then I saw the finish line and it read 19:48.  I immediately realized my mistake and sprinted for the line, only to fall a little short and come in at 20:03.  Shucks.  Had I set the watch to pace me to a 20 minute 5k, I'm sure I never would have been able to keep up mentally.  But due to my mistake, I set a 54 second PR and almost broke 20.

And I've decided resting for a race is for the birds.  I did a 750m/17mile/5k sprint two days before the 5k, ran 9 miles and swam 45 minutes on Monday, and biked 22 miles Tuesday morning, 12 hours before the race.  And it was 90 degrees.  And I had a piece of fried chicken for dinner 45 minutes before the race.  There's my new pre-race routine!

My stand-alone 5k does make me a little disappointed in my 5k efforts during tris.  My best during a tri is 23 minutes give or take.  I saw another thread where people say I should be capable to doing my stand-alone time plus 30 seconds to a minute.  I must be biking too hard, or wimping out on the run.