Rails, Unicorn, Concurrent Requests Breaks app - ruby-on-rails

Question

I have a Ruby on Rails app that I deployed recently and ran into a bottlenecking issue when too many users tried to use it. It's a simple game stats application. A user enters his name, the app makes an API call, and it returns the user's stats. It works perfectly when there are only a few users. When more users started using it though, it creates an insufferable lag, sometimes of up to 5 minutes per request. Therefore, I added unicorn to my Gemfile, set up a Procfile, and deployed it. Now, if there are two simultaneous requests, it crashes the app. I thought unicorn was meant to handle concurrent requests, not destroy them? At least before, my requests were still processing, albeit with a delay. What am I doing wrong here?
Here is the Procfile I used:
web: bundle exec unicorn -p $PORT -c ./config/unicorn.rb
Here is my unicorn file:
worker_processes 3
timeout 30
preload_app true
before_fork do |server, worker|
Signal.trap 'TERM' do
puts 'Unicorn master intercepting TERM and sending myself QUIT instead'
Process.kill 'QUIT', Process.pid
end
defined?(ActiveRecord::Base) and
ActiveRecord::Base.connection.disconnect!
end
after_fork do |server, worker|
Signal.trap 'TERM' do
puts 'Unicorn worker intercepting TERM and doing nothing. Wait for master to sent QUIT'
end
defined?(ActiveRecord::Base) and
ActiveRecord::Base.establish_connection
end