I hope by this you don't mean that because you don't do as big a volume of cakes as others that you shouldn't get paid just as well for the time you do spend.

If your talent is equal to that of a busier baker and you can produce an equally good product, then you should be able to get just as much for this cake as someone who would do this cake and a dozen others. If it took you longer to do than it took them, then you would get less per hour, but you should be able to charge the same total. You just need to know if the amount you would make per hour is worth spending the time doing this cake instead if spending the time doing something else instead.