Registration does not put you in the corral. This does. Set it up the day you register, not at 7:40 on race morning.
Any loop of 4.167 miles or more counts. You never have to hit the number exactly, so aim for 4.2 on your watch to be safe. Record each loop as its own activity. Start your watch at or after the top of the hour, never before. The file's own timestamps decide which loop it is. Screenshots are not accepted.
Garmin: open the activity in Garmin Connect on the web, select the gear icon, then Export Original or Export to GPX.
Coros: open the activity in the Coros app, select the share icon, then export as FIT or GPX.
Strava: open the activity on strava.com in a browser, select the three dots, then Export GPX or Export Original.
Apple Watch: use an export app such as HealthFit to save the workout as a FIT file.
You can log loops late. A loop logged after the race still counts if its timestamps are right.
Tap this when your night is done so the corral knows. Going out is the ordinary result.