Won't my scarf get smaller if I knit 2 together?

I've knitted a few scarves now, but I really wanted to create a pretty pattern ("holes" in it). However, when I slip a stitch and knit two, then pass the slip stitch over the 2nd stitch off the right-hand needle, I'm a few stitches short - my scarf is shrinking! How can I keep the width but still have my pattern?