[EricS]

I had a problem similar to with with a speaker cabinet build I did a few years ago. I was using Baltic Birch plywood and one of my cuts was off by a very small fraction. I was able to cut a very thin "shim" with my table saw - just a thin strip and drop it down into the gap. A little glue on each side and it was a perfect fit. I would think the same technique might work here. Use a thin piece of wood or veneer and just cut a narrow strip and glue it in place. Make sure it is a bit "thicker" than it needs to be so it can be sanded down so it is level and smooth.