The BSR helps to regulate your stitches but it is not foolproof. It prevents me from getting the micro stitches which was my main problem. Are you using BSR #1 or #2 ? I can't get the hang of sewing without a foot pedal. I believe the machine has about a 3 second delay before it starts to sew which can result in a larger beginning stitch. On a whole, my stitches are pretty regular.
Is the red light on when you begin to sew? If the red light is not on, then the BSR is not working. Does your dealer offer free lessons? I still go to my Bernina club once a month to learn new things.