Classic Shirt

I am stumped on step 1 of the directions for the classic shirt! The pattern says to cut a 1 inch planket... but then it goes on to say to baste 1/2 in... then add a 1 inch piece of interfacing to that basting line. I already cut the piece off. If I add the interfacing on at that 1/2 inch mark, fold over, and then stich onto the shirt with a 1/2 seam... I'm out of planket! What am I missing? (I have been sewing for many years but this is my first time really using a pattern for something) Who can help me?