A stitch in the ditch foot has a bar in the center rather than the right side.
If your walking foot has a very small stitch, it could be one of 2 things. Your fabric is too heavy in the front and it doesn't have a chance to feed through at the proper feed. Hold the fabric up so the walking foot isn't doing all the work. Or it could be foot pressure. SOme of the sewing machines has knob at the top that will put more pressure on your foot giving it a chance for even feed.
I hope this helps.