There's an easier way to check stock, assuming you're using chrome here are the steps and apologize if it's hard to follow. I got a billions things to do before I goto sleep but wanted to help out.
Open developer tools (look for it in the options)
Click Network
Now goto Walmart page where the item is using your browser. Click Buy in store
Go back to developer tools and you should see "availability" from the list
Click preview
expand the options until you see inventory.
The attached picture is for Kwik-E-Mart. I added 1+total inventory and I'm unable to checkout, shows OOS. Put in the right inventory and I can checkout
The Porsche GT3 shows up as 2 in stock. Try adding 3 and going through the checkout process, it won't work. Try adding 2 and it will go through.