race days are often more demanding than people think. you might get up earlier than you normally do on a weekend or even weekday. commute someplace half asleep. park. walk to race site. maybe go by packet pickup on the day. figure out how to pin on a number. get into race clothes, find a place to put belongings. warm up. stand around and wait for the start. run hard in mid-day elements. you may feel stressed and tense.
vs. practice, depending how you do it, you walk out the front door, do some stretches, and off you go. or you go to a track or park, park car, probably start running right there. probably relaxed. you might notice how you're doing or feeling but not a lot is riding on the practice day.
IMO if you want race day more like practice, you need efficiencies. do packet pickup before race day if possible. perhaps stay in a hotel near the start line. have your spouse drive you, park car, watch your stuff. try to narrow it down as much as possible to "show up and run" -- like practice. less work, less running about doing errands.
last, you may be getting tense and that, to me, is a combination of timing your stretching, being in a space where you can get loose before the race as opposed to are boxed all in crowded with people, and perhaps a little meditation at the line. just chill and run. older i got the more i found "smooth is fast." it's counter-intuitive but eyes-bulging, hands-balled intensity makes you tenser and slower. relax, breath, work your pace and to pass people steadily.