A family of Microsoft word processing software products for creating web, email, and print documents.
Doug's solution is good as a quick fix for a merge output that already exists. To avoid having to do that in the future, DO NOT use the 5160 "template" (actually a document) downloaded from the Avery site.
The Label Options dialog that Word displays when you click Start Mail Merge on the Mailings ribbon lets you select the 5160 label type, whose data is built into Word.
When you use this definition, Word's internal programming tells it to ignore the margin settings that would otherwise cause the message you had to deal with.
If your document full of labels was created without using the mail merge feature, you can convert it to a mail merge data source by the procedure in https://www.gmayor.com/convert_labels_into_mail_merge.htm. That will make it much easier to edit, add, or remove entries in the future.