Dear Colette,
Thanks for reaching out.
Generally, this issue is due to using multiple Google accounts under the same Chrome browser. Google can't handle when multiple accounts are logged in, and Chrome extensions, such as Labelmaker, don't work well.
SOLUTION:
Since you are using multiple Google accounts I recommend creating a new profile in Google Chrome with the account you are using Labelmaker with. This will make sure it'll detect the right google sheet for the merge fields. It takes only 1 minute to set up.
Let me know if it works,
Lucy