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?

<img src="https://i.sstatic.net/Odv4r.png" width="200">

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?