I'm doing 2 margarita cakes - just finished up the first one and had a hard time getting the sugar only on the 'rim' of the cake, it also landed in the sides of the cake (all buttercream)
How do I only get the sugar to rim the top and not fall and stick into the sides?
You could try using a disposable piping bag and clipping the corner enough so the sugar spills out controlled.Then you have some sort of way to keep the sugar in one area as opposed to it getting everywhere.
When I make my margarita cakes, I pipe a strip of piping gel around the rim before sprinkling the sugar on. The sugar sticks to the piping gel immediately and doesn't fall down the sides. You can see one of them here. http://cakesbycarla.com/Photogallery/margaritaglass.jpg
Just a thought - but could you do like some rolled buttercream and roll that in the sugar and then press that on rather than sprinking the sugar right on the cake?
Aww, cake turned out cute!
A squeeze bottle is also good for controlled application, for future reference.