Printing Document sizes

I am a seamstress and I buy a lot of PDF patterns which the designers prefer using adobe for printing out the patterns. My problem is my pattern pieces never line up just right and I think I've figured out why. My current settings are for letter but under Document on the print window it lists: 7.0 x 10. and 8.5 x 11. I'm wondering if that added 7x10 is what is throwing off the alignment of my pieces. I've pressed every single thing I could in the print window but nothing takes away that 7x10 so it only shows the 8.5 x 11. Is there a way to set it so it only prints 8.5 x 11? TIA