HI,
To help keep my sprocket centered as I torqued the bolts in criss cross fashion, I wedge cut down paper clips between the center of the sprocket and the hub of the wheel....That way the sprocket won't shift as I tighten the bolts...You can use other things than paper clips but it is what I had handy and it seemed to fill the gap and center the sprocket pretty well (I left the small metal pieces in even after I tightened the bolts....just used an end nipper to cut them flush with the sprocket face....I could have taken needle nose pliers and tried to take them out but they are tight and I figure they will help keep the sprocket relatively well centered (the thought has entered my mind that if a piece fell out it could puncture a tire but they haven't gone anywhere yet.
Hope this helps you.
Andrew