What do you call a "fancy" goldfish? Some of the types with short, fat, bodies have a tendency to swim bladder problems as their digestive system leaves something to be desired as a result of their breeding.
38L is not big enough for 2 goldfish as they grow large and produce a lot of waste. When you upgrade to a bigger tank, look at around 120L at least (a standard 3ft tank) if you plan to have 3 or more.
Comets are best in a pond. Those with long flowing tails, or over developed eyes, that cannot swim very far or fast, are OK in slightly smaller tanks.