Are goldfish as prizes not banned now? Makes me so so angry when they do this.
Goldfish can live for decades if treated correctly, unfortunately so many don't because there are so many myths circulated about them (and because we all grew up with goldfish using incredibly unsuitable tanks).
To flourish they need at least 10 gallons of water per fish in a filtered aquarium. (Ideally you should have 20 gallons for the first fish and 10 gallons for each subsequent goldfish). There is a popular myth that they only grow to a suitable size of the tank and then stop - but in reality they become stunted and their outsides stop growing, but their insides carry on growing causing a painful and prolonged death.
Even a "small" fancy goldfish comes massive at adult stage. Pop to a reputable fish shop and see the adult fancies there - they're like massive cooking apples with fins. Easy to see then why tiny tanks are so unsuitable. Also, they are very messy fish so need adequate filtration and regular water changes to keep the healthy.
The scooby tank listed there is only 3 gallons. Please consider getting a larger tank. Also, as you have a brand new tank, you will probably need far more regular water changes than weekly until the friendly bacteria builds up in your tank - if this is neglected, deadly ammonia can build up in the tank and kill your fish (also known as "New Tank Syndrome"). Google for "Cycling with Fish" for more info (this refers to the ammonia cycle, not a pedal cycle!)
Some more information here:
Practical Fishkeeping Goldfish FAQ
Make a Goldfish Live for Decades
cycling with fish