You're putting two stitches into the one on the row below, so you're getting two extra stitches. You're not using a stitch that's already on the left needle.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry