the gcd you have provided outputs wrong result i think and for some inputs it outputs error
(attached a photo with x=12 y=4 so the gcd should be 4)
pow_in must be in one-hot representation, i.e. exactly one bit of pow_in must be 1.
The correct representation of 0 in one-hot representation is 0001, not 0000.
On a separate note, you seem to have added two input ports for done_in and pow_in. Do not do this, it will cause your file to be incompatible with the automated validation and grading system. If you need to use a constant value as an input signal, use the Constant component from the Wiring library, as mentioned in instruction #5.