Having authen_LTI.conf around and also having the same information cut and pasted into course.conf is probably not wise. Any variables set in course.conf will override what is loaded earlier (in this case authen_LTI.conf and possibly localOverrides.conf), so you run the risk of changing something in authen_LTI.conf, and not having it take effect because it is later overwritten by course.conf.
My recommendation is that any settings that will be the same for all courses be put in localOverrides.conf and authen_LTI.conf, and only things that will be different for an individual course be put in course.conf.
This leads me to the first thing to check: if $LTIBasicConsumerSecret is set in course.conf, then this is the value that will be used. Make sure that this string matches exactly what you set in Canvas. For debugging purposes. I would start with a secret that only involves numbers and letters. I don't think symbols should cause a problem, but this eliminates one possible complication.
A couple of other things:
Make sure that the consumer key is set in Canvas. It can be set to anything, but I know when I set up LTI, WeBWorK didn't like having a blank key.
Try the URL in Canvas with and without the slash at the end. I have mine set up with the slash at the end (i.e. https://webwork.yourschool.edu/webwork2/coursename/), but I can't remember how picky it is about this.