Good day, Molly5.
I can give you a quick run through on how to check if it was correctly set up.
When you set up the sub-accounts, let's just make sure the Is sub-account option is checked, then the correct parent account is chosen.
Please check the screenshots as your reference.
I've got you an article for future reference: About bank or credit card sub-account setup.
Feel free to leave a comment if you have other concerns. Have a nice day!