Ok well first, we need to be specific on what shark you are talking about. "Banded Cat Shark" is a term of which most people don't even realize the distinction between the different species this all-too-common name covers. For example, that name alone can reference to either a Brown Banded Bamboo Shark (Chiloscyllium punctatum), a Banded Sand Catshark (Atelomycterus fasciatus), or a variety of other "Catsharks". More than likely you mean a Brown Banded Bamboo shark, which, along with many other sharks, is known by several "common" names. Thus the importance of always knowing the scientific name of your animal, as "common" names can actually refer to a number of species.
Keeping an egg, and later, the newly hatched pup in a 55gal is ok - for a little while - . I do this quite often actually, as it gives me the opportunity to more easily observe new pups and get them started on feeding and gain their bearings with swimming and allows me to closely monitor their health and activity levels without having to hunt them down in larger tanks. But just so long as you know that this situation can only be temporary, and will not suffice much longer than the first 6-8 months, as within the first year, healthy and well fed bamboo pups can grow at an alarming rate of anywhere between 5-9 inches, and rarely (though it does happen), can pass that by an inch or two.
You can expect your pup to wriggle out of it's casing at a petite 5 1/2 - 6 1/2 inches, which works fine with a 55gal to start with. However, I'd highly suggest getting that larger tank up and cycling right now to allow it time to mature, as you won't have long before your little one needs much more space. And when it comes to the "needing a 200gal"... ummm think more like 400.