I'm not sure what the teacher was trying to tell you either, but if you have made sure the quilt is square and you put your binding even with the cut edge of the quilt, pin, pin, pin, and when you sew, try using the longest stitch you have and then check it. If it looks o.k. restitch using the normal stitch length and if not, you can easily remove the areas that need adjustment and not the area that looks right. I have to do this a few times and after I got used to binding, I could just attach the binding without the "practice" run.
Hang in there, you will get it. Pam