Yep, centering is tricky particularly on round, or oddly shaped pieces. Not too hard with squareish pieces, just scribe lines that connect the corners and stick your centers where the lines meet. but on a round piece you have to do geometry on the end grain with a scribe and compass to get close, and it's hard to feel scribed lines on end grain.
I usually just tried by guess and spun the piece by hand with the tool rest set closeish and checked out the change in distance to the tool rest. Then move the centers just a hair to get as close as you can before spinning it at a low speed to gouge it down to round. It seems a bitscarrey at first but as long as you take it slow it'll be fun. Tom
