|Knit hems can be a real hassle. Sometimes your needle wants to shove the material all the way down into the bottom feeding bobbin.
Time to improvise. Cut a newspaper into strips and just lie it down on top of your material and stitch over it. Its easily ripped off afterwards, and does't leave any sticky residue. If newspaper doesn't work, try construction paper, or old cards.
If those methods don't work, spray on starch might be a possibility........... or scraps of interfacing, or even scraps of tissue paper left over from when you cut out the pattern.