Hi, Poshlloyd!
Sorry to hear you have to cut your walk. I tried to search for convenient itinerary for you on Sat., 07th Sept., but constant error was shown on bus companies web sites (Alsa, Movelia). So I could only get the trains timetable.
You can decide to go back to Logrono (50kms) or forward to Burgos (75kms) with local buses. From Logrono to Bilbao there are three trains on Saturday: 10:23, 17:18, 18:35, it takes approx. 2:30 - 2:45 hrs. From Burgos there are two trains: 11:24 and 19:25 and the ride takes 2:30hrs.
Hope that will be of some help!