Which of the following is the major organic product when acetone, CH$_3$COCH$_3$, is allowed to react with hydrogen cyanide in the presence of a catalytic amount of sodium cyanide?

The correct answer is (B), rather unsurprisingly. However, I got this answer without using the catalytic sodium cyanide. In my proposed mechanism, the dissociated proton from HCN activates the carbonyl, which facilitates the nucleophilic attack of CN$^-$.

What role does the NaCN play?