Following on from McClef, the graduates wearing kilts at St. Andrews simply replace the bow tie with a white one. The PC is a pretty formal dress as it is. Three things from your photo, you shouldn't wear a "bunnet" (headgear) to a formal event and it is not usual to wear a buttonhole with a PC jacket. Also a more formal sporan with a silver cantle would be expected for "white tie". Otherwise your outfit looks great, just wear a white tie with the wing collar.