Jaws, I'm not sure I agree with a 55 not being a starter tank. I think noni will have a much easier time keeping the larger volume of water stable. A 10 gallon will sink or swim very quickly, with very little reaction time available to deal with any problem.
The problem here as I see it, is that noni walked into the fish department, received either no advice or extremely poor advice, and the fish place ended up selling her/him a whole bunch of stuff he/she was way undereducated to make good buying decisions on. How dare they; but they do it to novice fishkeepers every day of the week.
Noni, welcome to the world of fishkeeping. The folks here, including jaws69, who is a nice and knowledgeable forum member and frequent contributor here, are ready and willing to help with advice to get you up and running. If you listen to the people here, especially the mods, who have a lot of experience in fishkeeping, you'll be fine.
Okay... first things first.... Read the stickies at the top of the beginner forum. Pay careful attention, maybe make some notes if that's your style, it's very important information.
Secondly, I concur with jaws that the fish they sold you are totally inappropriate for a beginner with a just-set-up tank. You need to decide between cycling fishless or fish-in. When you have read the stickies you will understand what that means, so keep that question in mind as you read. I would take the fish back-- they should accept them since they basically set you up for failure by selling you a new tank and all those fish at the same time-- and use the money or store credit to get test kits. You will need tests for ammonia, nitrite, and nitrate during your tank's cycling as well as later.
If you just have a few fish left and would prefer trying to save them and rebuild from this point on, you need to do partial water changes every other day at least. You can take a water sample to the store and have them test it. Make them tell you the results for ammonia, nitrite, and nitrate. DO NOT let them tell you it's 'fine' or 'not good' or some other generalization. You need numbers. Write them down, you will need them when you post on the forum and ask for advice. Get the test kits if at all possible so you can get your own results quickly instead of having to run to the fish store.
I'd go ahead and do a water change immediately, maybe 30-40%, being sure to match the water temperature and add the appropriate amount of dechlorinator. Your fish are probably dying of ammonia and/or nitrite poisoning. A water change will help.
They should have sold you a few zebra danios or some other hardy fish if you were going to cycle your tank with fish. I hope that the ones you have left can survive the cycle, but if they don't, try not to beat yourself up over it, this happens to new fishkeepers alot. Stores tend a lot of times to sell people inappropriate fish and other unnecessary or even harmful stuff. But you can come out on top over time. Coming here was a gret decision on your part. I know it saved me and my fish a lot of misery.