I had the same issue with "sink" on mine... live and learn ! I'm guessing I simply should have left it sit for a few weeks before filling, priming and sanding again. Just to give it all tie to settle. Guessing the glue might be pulling the dowel in as it cures... or the wood slightly swells with the moisture of the glue and then contracts again ?
That's an awesome blue. Looks like you could dive into into it !