How to change Label margins

I have a registered database (spreadsheet). I have mail merged 400 letters with correct names, etc. in the bodies of the letters. Everything ok there.
I am trying to create mailing labels. I am using Maco labels which they say are the same dimensions as Avery 5960. I decided to print out just the first page (30 labels) to make sure everything was ok. It was except maybe 1/16" of the left margin of the leftmost column doesn’t print. I want to increase the margin for that column of addresses by about 1/16", but when I try, only the first (uppermost, leftmost) address label is affected when I print a test sheet. When I Edit>Select All, it is the only one selected. I’d like to select that first, leftmost column and then somehow change the margin a bit.