Am I sinful for publishing excerpts from a book and then sending them to others without prior knowledge that it is not permissible, knowing that I can delete it after discovering the matter?

You bear no sin for violating the program's terms unintentionally or out of ignorance. A servant is not held accountable for mistakes, as Allah Almighty says: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended." Allah has indeed removed accountability from this Ummah for errors and forgetfulness.

You are not obligated to pay any financial compensation to the program owners as long as your actions did not cause them material harm. If you wish to be cautious, you may seek their forgiveness. If you are able to delete the book from those to whom you sent it, then do so.