Dear Cari,
Thanks a lot for sharing your spreadsheet with me. I did a copy to avoid modifying your own spreadsheet.
The issue come from your header row: we can only detect merge fields if there is one header row.
n your example, it works well if I deleted the first 2 rows and I only kept:
"Teacher Color YXS YS YM YL YXL A-S A-M A-L A-XL A-XXL A-XXXL Amount Paid" (see screenshot below)
Let me know if it helps,
Lucy