The rvm installer puts different things in your .bashrc and .bash_profile files, which means it is loaded differently in login shells and interactive shells.
Try running rvm use default. If you get a message telling you “RVM is not a function, selecting rubies with ‘rvm use …’ will not work” then you’re not in a login shell.
According to a blog post called “Bundler and rvm: remember about login shell” not running in a login shell can also cause the issue you’re seeing, although I’ve not been able to replicate it here.
Hopefully that’s put you on the right track. Good luck!