Looks like I should have booked Raleigh, Charlotte or Durham to stay the Sunday night after the Martinsville race (Oct 30) rather than Greensboro. Wish I'd done my homework. Will know better next year.

Greensboro is an deserted island for some reason.  THere are a few good agencies in the area

Check your cancellation policy.  Most places allow you to cancel your reservations up to the day you check in. Then rebook for Raleigh or Charllotte.  If not, either are not far from Greensboro.