It sounds like you are taking the right steps to get Bentley trained, I wouldn't be too hard on yourself. Bentley is a Terrier and they are very stubborn ~ Trust me I am still working on potty training, and my Pnut is 3 years old!
I would just work with him more. Everyday you should work with him, I am not sure "how" but if you look in the "training threads" I'm sure you will be able to find something..Or you can post your question there.
Good luck! Just keep up with the training and I'm sure he will catch on soon!