Making a shelf

[quakerboy]

So, I am in the process of making a shelf that extends out both ways from a corner.

I reasoned that, if the corner were 90 degrees, I could cut one board at 45 degrees, flip one side, and the pieces would match and fit into the corner.

So when the actual angle was 95, figured I should cut it at 47.5 degrees.

This did not work out. The back corner is in the right spot, but at the front of the shelf, they overlap.

What did I do wrong?