If your stitches are getting small (and I'm assuming that you're not trying to free motion quilt) then your quilt is probably getting hung up on something, or the weight of the quilt is keeping it from moving smoothly. Use a walking foot or SID foot, keep the feed dogs up, and be sure to support your quilt all around. Before I got a longarm, I quilted most of my big quilts in sections (using Marti Michell's book as a guide). Good luck!