Does the shark look like this?
Tropical fish (the shark) and coldwater fish shouldn't be mixed. The temperature of the water is important to the health of the fish and so putting goldfish in warm water or tropical fish in cooler/cold/room temperature water will often cause problems. Larger coldwater fish such as goldfish (yes, goldfish do get big and no, there is no such thing as a "mini" or small variety suitable for a 2 gallon tank) will produce a lot of waste and make the water extra toxic extra fast. They can often cope (but not thrive) under these conditions but smaller fish and most tropical fish will really suffer. Plus goldfish can be right bullies, even when small.
From the sound of things, your tank wasn't "cycled" either. This is a word we use to mean building up a sustainable eco-system in a fish tank. This requires a lot of care and attention and is
essential for the health and survival of the fish. An un-cycled tank (usually one that has been newly set up and is under 2 months old) will quickly become a death trap if you put fish in without considerable care. This is because when the fish poo and wee there isn't a proper eco-system of bacteria in the tank to nutralise the toxic chemicals produced by the fish. Some fish will survive this process (called a "fish-in cycle" because it uses the actual fish to help grow the bacteria) but many fish will die and all fish will be harmed unless the cycle is conducted with daily water tests and very large water changes to keep the chemicals diluted until the bacteria can grow.
Please read the information here - there is a full description of what the cycle is, how it works and how it is managed.
Do you have a filter? Is your tank heated? What temp is it? Are you using dechlorinator/tap water conditioner? Any medications?
A fish that jumps is normally a sign of two things - a tank that is too small and water that isn't good for them.
The shark (depending on what species it actually is) will probably require a tank that is around
30-40 gallons, if not more, as they get to around 6 inches (sometimes bigger) and need a lot of space to swim and establish their territory. Goldfish (even the smallest varieties) need 20-30 gallons just for one. They should also be kept in small groups as they are very sociable and so you'd really need a 30-40 gallon tank just for a pair of fancy goldfish (the ones with the long fins and compact bodies). A comet, common or shubunkin goldfish (the ones with shorter fins and straight bodies) get much, much larger and would need a 30-40 gallon tank until they got to about 4-5 inches and then would need to be moved into a large pond.
A small tank will stunt the fish, causing organ damage and generally make their lives very miserable. It almost inevitably leads to an early death, and a painful one at that.
Summary of some things that could have gone wrong -
+ Poisoned from un-cycled tank
+ Damage from the jump and from being out of water
+ Sick when purchased
+ Stress of being moved to new home
+ Bullied/stressed by other fish
Check out the link I posted - you've really rushed into fish keeping and it sounds like you have been lied to and badly advised by the shop you got your fish and supplies from. It's great that you've found this forum - let us know if you need anymore help or have any questions!