rails won't execute for newly created app

I'm struggling to get going with rails, so apologies for being a n00b. I've installed and uninstalled Ruby and all of my gems several times now and am still having problems getting rails to launch. If I do...

$ rails new sample_app
...
$ cd sample_app
...
$ bundle install
...
$ rails s
Could not find rake-10.5.0 in any of the sources
Run `bundle install` to install missing gems.
$ gem install rake -v 10.5.0
Successfully installed rake-10.5.0
Parsing documentation for rake-10.5.0
Installing ri documentation for rake-10.5.0
Done installing documentation for rake after 0 seconds
1 gem installed
$ rails s
Could not find rake-10.5.0 in any of the sources
Run `bundle install` to install missing gems.
$ rails --version
Could not find rake-10.5.0 in any of the sources
Run `bundle install` to install missing gems.

When I do gem list I see rake 10.5 is installed. I'm running Ruby 2.3.0 that I installed using rbenv. Running bundle install or bundle update as it indicates doesn't help. Suggestions?