All sorts of things one could do here, some of which depend on when the course was originally measured.
1. Truncate course at the 3 mile mark. If the course was measured earlier this year and the counts from the start to the 3 mile mark are within tolerance, you simply use those measurements and resumbit the application with a new map, and you have a new course with a 2022 expiration. If the course was measured before this year, the new course would expire ten years after the measurements were first submitted for certification.
2. Shorten the start/finish spur. This could be done with a steel tape. Move the start and finish approximately 86 meters toward the mile mark. Move the mile and 2 mile marks 86 meters toward the finish. Draw new map. Done. Again, if it's an adjustment of a course measured earlier this year, it expires in 2022. Otherwise, it expires ten years from when first submitted for certification.
3. A combination of the above- depending, of course, on the logistics of the start/finish.
I don't see any reason to perform another ride in any case, unless by doing so you would extend the course life for a full ten years. We've established that one can do that to an expired course. Can you extend the expiration of an active course with one ride?