WallowinWasabi

Thank you! I didn't even notice that the bottom of the receipt was a different receipt number. I was going crazy lol. And thank you for taking the time to respond

Not sure what you mean by leaving the interview location.  You cannot pay the fee until the visa is in hand.  You will not walk out of the "Interview location" (US Consulate) with the visa in hand.  It will arrive affixed to a page of the passport, some days later.

No. You cannot pay until you have your passport back in hand as you need 2 documents numbers which are on the visa foil in your passport. 
Pay only after receiving back your passport , but you can pay either before or after you enter the US.  Processing of your passed GC will not commence until BOTH the fee is paid AND you have entered the US on your immigrant visa 

You get a year on the 'temporary green card' when you enter the US. So you don't actually need the physical plastic GC right away, and you could wait 6 months or so to pay the fee if money was tight. 

Yes, up to you when you want to pay it. Your immigrant visa turns into temporary green card good for a year after you activate it at POE. To get the real plastic one, you pay the fee - takes them about 90 days to produce and mail you the card. 

The way I read it you used to have a B and used that.

If  you entered the USA from Canada using the Canada Visitor Privilege, you would not have a visa number.  Do you see any appropriate selection in visa classification drop down?  If not then you were never issued a visa.