I'm a beginning knitter, and I'm trying to knit a scarf to match a hat I made for my son. I'm doing it in stockinette stitch edged with a 5 stitch border of garter stitch. On the left side, right between the 5th knit stitch and the next purl stitch it is not tight, and is just making a ladder, and I can't tighten it up. The right side is fine, it's the left side that's always loose. I'm using size 10 needles and some Red Heart worsted yarn. Can someone tell me how to fix this, please? I'm making sure that I'm not doing a yarn over, and it's not a dropped stitch.