Hi mpeterson11!
Welcome to the QuickBooks Community! I'll explain what happened to your purchase order, so you'll be guided with your next steps.
When you copy a purchase order to a bill and receive the full quantity of the item, that item will be marked as closed. You can't remove the checkmark. You'll want to open the linked transaction and change the quantity or remove the item instead. Or, you can delete the linked transaction by clicking More > Delete.
I'd like to add these articles for your additional reference:
You can always reach back out if you need more in help managing your transactions. Have a great weekend!