i agree. there is NO goldfish that will fit happily in your tengallon tank for very long. they grow fast, and they grow BIG.
i've had my 12 cent "feeder" comet goldfish for only one year, and he's at least 6 times the size he was when i got hom, and therefore already too big for a 20gallon.
these are bred to be FED to other fish, and if not fed to other fish, they're bred to be PONDfish.. and by pond they mean several hundred gallons of water with only a few other comet goldfish.
the fancy goldfish are different, but not much. they grow just as fast, and only a couple inches smaller, still, you need about 20 gallons for the first fish, and about ten gallons per fish after that.
its not just size that's a problem, its also waste, being so oddly shaped, and also since they're coldwater fish, they arent very efficient eaters, and they produce a LOT of waste.
in your 10 gallon tank, you're going to want tropical fish, which need a heater (yes your tetras should have a heater) and goldfish should NOT be in a tank with a heater.
i suggest you take the comet back. and if you can, take the 1 gallon tank back too. theres next to nothing that will fit in a 1 gallon tank. and unless you have a pond for your comet, he's just going to die.. if you put him in your ten gallon tank, he may grow fast enough to eat all your other fish and THEN die. either way, its not a good situation.