Rails does not find gem, although it is installed - ruby-on-rails

Question

I hope somebody can help, I am really confused about this. I want to use the gem svg-graph (github) within my rails app. But require 'svggraph' gives me this error: cannot load such file -- svg-graph, which I don't understand as running a script inside the app folder requiring the gem runs perfectly.
I have gem 'svg-graph' within my Gemfile and bundle installs ran successfully.
gem which svggraph gives me /Users/Username/.rvm/gems/ruby-2.3.3/gems/svg-graph-2.1.1/lib/svggraph.rb.
If it helps here's my output of gem env
RubyGems Environment:
- RUBYGEMS VERSION: 2.6.10
- RUBY VERSION: 2.3.3 (2016-11-21 patchlevel 222) [x86_64-darwin16]
- INSTALLATION DIRECTORY: /Users/Username/.rvm/gems/ruby-2.3.3
- USER INSTALLATION DIRECTORY: /Users/Username/.gem/ruby/2.3.0
- RUBY EXECUTABLE: /Users/Username/.rvm/rubies/ruby-2.3.3/bin/ruby
- EXECUTABLE DIRECTORY: /Users/Username/.rvm/gems/ruby-2.3.3/bin
- SPEC CACHE DIRECTORY: /Users/Username/.gem/specs
- SYSTEM CONFIGURATION DIRECTORY: /Users/Username/.rvm/rubies/ruby-2.3.3/etc
- RUBYGEMS PLATFORMS:
- ruby
- x86_64-darwin-16
- GEM PATHS:
- /Users/Username/.rvm/gems/ruby-2.3.3
- /Users/Username/.rvm/gems/ruby-2.3.3#global
- GEM CONFIGURATION:
- :update_sources => true
- :verbose => true
- :backtrace => false
- :bulk_threshold => 1000
- REMOTE SOURCES:
- https://rubygems.org/
- SHELL PATH:
- /Users/Username/.rvm/gems/ruby-2.3.3/bin
- /Users/Username/.rvm/gems/ruby-2.3.3#global/bin
- /Users/Username/.rvm/rubies/ruby-2.3.3/bin
- /usr/bin
- /bin
- /usr/sbin
- /sbin
- /usr/local/bin
- /opt/X11/bin
- /usr/local/git/bin
- /usr/local/go/bin
- /usr/local/MacGPG2/bin
- /Library/TeX/texbin
- /Us
ers/Username/.rvm/bin