Origami imperfection 1

Let the original square be divided up into 16 equal squares. Then the quarter-square of Step 1 will consist of 4 of the 16 little squares, and the two triangular corners of Step 3 will take up 2 of those little squares, and the diagonal of Step 3 will take up the remaining 2 little squares, as pictured below.

Then $\angle AOB = \tan^{-1} \frac{1}{1}$ and $\angle BOC = \tan^{-1} \frac{2}{1}$ , which makes $\angle AOC = \tan^{-1} \frac{1}{1} + \tan^{-1} \frac{2}{1} \approx 108.43494882°$

This is close to the interior angle of a regular pentagon, which is actually $\frac{(5 - 2)180°}{5} = 108°$ .

This makes the difference $108.43494882° - 108° = \boxed{0.43494882}°$ .