Zen Knitting

The most likely mistake I can think of is that you are not starting your row correctly for double crochet and are adding a stitch. It is odd that this mistake would only affect one side of your work though. Usually a person would be doing this incorrectly on both ends of the piece, but it is a possibility.

When you start a row of single crochet, you chain one, turn the work, and then start working in the first available space. A row of double crochet is chain three, turn, and work in the second space. If you were to work a double crochet into the first space, you would effectively be adding stitches to your work and making it wider. Perhaps you are doing the turn correctly on one side of the project, and working in the wrong stitch at the other?

Incorrect turns or missed chains can also decrease your work. When you leave off a chain in your turn, your stitch will be too short compared to the row and you may skip it when you work back across. This would cause a lost stitch. If you are skipping too far into your row to start your stitches it would decrease your row as well.

If you are absolutely sure that you are turning correctly and that you’re not missing stitches somewhere along the row by mistake, you may not really have a problem at all. A blanket is a large, usually heavy project. Sometimes this weight and size can distort your fabric while you are working on it. This kind of thing can be corrected by supporting the work as much as you can while you are crocheting and blocking the work when you are finished. To know if this is all your problem is, count your stitches in your rows. Counting like this is tedious on a blanket, but so is ripping out stitches and reworking them.