Claim duress......sounds to me like it was under duress. Better do something tomorrow....don't wait.
Come to think of it.....it is against the law in Virginia to landlock a parcel of land. I don't know about the laws in your state but maybe that is why they were trying to get this resolved quickly?
Make them put it in writing exactly where the access to their property will be across your land. OR make them buy the access and deed that portion of your property to them.
Definitely do something tommorrow about it....sorry this happened to you.