Why this current regulator won't regulates?
It looks like the problem is the values of R6 and R7. The voltage divider ratio is \$\frac{R7}{R6 + R7}\$, which works out to \$\frac{1.8k}{18k + 1.8k} = 0.091.\$ That gives you about 45.5mA, which is close to what you see. You actually want a ratio of 0.1. Add a 220-ohm resistor in series below R7 and you'll get much closer to your ideal value.