https://www.judycoatesperez.com/wp-content/uploads/2020/08/Best-COVID-Mask-Instructions.pdf
Mask designs are printed oversize to allow for fabric shrinkage. You can also easily add a nose wire after the mask has been turned inside out. Slip nose wire inside and center at top stitched edge, hold in place and stitch along edge of mask. When you come to the nose wire, turn fabric, stitch down 1/4" and then along the length of the nose wire, then turn mask stitch 1/4" up to enclose the wire and continue stitching around edge of mask.