Another factor, in the size of stitches, is HOW you make them. It's easier to make small stitches, if you insert the needle straight down into the quilt, all the way through the layers. Then come straight up, from the back/bottom. This is a bit more tedious but will result in smaller, more controlled stitches. If you've ever done counted cross stitch, the technique is much the same.
That said, there's nothing wrong with larger stitches!
