What am I missing to define a variable from a page object? Getting undefined error in watir-webdriver - watir-webdriver

Question

I'm trying to create a page object for the forms I'm automating and getting undefined local variable or method for 'checkout_form', though I thought I've already defined the variable.
This is my page object page:
require "page-object"
class CheckoutForm
include PageObject
# Checkout page
# Billing info
text_field(:billingfirst, :id => 'CheckOut_BillingTag_FirstName')
text_field(:billingmiddle, :id => 'CheckOut_BillingTag_MiddleInitial')
text_field(:billinglast, :id => 'CheckOut_BillingTag_Lastname')
text_field(:billingaddress, :id => 'CheckOut_BillingTag_Address1')
text_field(:billingaddress2, :id => 'CheckOut_BillingTag_Address2')
text_field(:billingcity, :id => 'CheckOut_BillingTag_City')
text_field(:billingstate, :id => 'CheckOut_BillingTag_State')
text_field(:billingzip, :id => 'CheckOut_BillingTag_ZipCode')
text_field(:billingphone, :id => 'CheckOut_BillingTag_Phone')
text_field(:billingemail, :id => 'CheckOut_BillingTag_Email')
def billing_info( billingfirst, billingmiddle, billinglast, billingaddress, billingaddress2, billingcity, billingstate, billingzip, billingphone, billingemail )
self.billingfirst = billingfirst
self.billingmiddle = billingmiddle
self.billinglast = billinglast
self.billingaddress = billingaddress
self.billingaddress2 = billingaddress2
self.billingcity = billingcity
self.billingstate = billingstate
self.billingzip = billingzip
self.billingphone = billingphone
self.billingemail = billingemail
end
end
On a different page that will use the page object I've added ' require_relative "checkout-form.rb" '
And there I set up the driver:
#b = Watir::Browser.new :ff
checkout_form = CheckoutForm.new(#b)
And interacting with the pageobject methods here:
checkout_form.billing_info.set 'Mike', 'L', 'Jones', '13677 Ruette Le Parc', 'Unit G', 'Del Mar', 'CA', '92014', 'aaaaa', 'mike.jones#gmail.com'