Looking at the picture, I noticed some of the needle holes looked larger than the others. I'm wondering if it's a problem with the needle. I used to teach quilting and one tip I always gave my students was this: When sewing with cotton, always, always, always use a sharp point needle. The newest rage at the time and still is are the Universal Point needles, but I always use Sharp Point needles when working with cotton. You might try that and see if it makes a difference.