B20DTH cam chain replacement

[Coxy]

On the B20DTH engine the camshaft chain and tensioner was severely worn.

On replacement I timed the camshafts to the dots and marked the camshaft sprocket (belt end). Whilst trying to undo the cam chain sprocket bolt (whilst holding the nut shaped flat on the cam) the bolt didn't undo, but the camshaft moved and the spanner holding the nut shaped flats didn't. All marks still line up again. Is this an issue? Would timing be affected. I was under the impression the camshaft was one piece and this couldn't happen.