Faye have you tested your water Conditions yet. its best to buy your own test kits for Ammonia, Nitrite, Nitrate and ph. As your tank is still in the early stages of the Nitogen Cycle which i asume you've read a article as a link was posted earlier. While your Ammonia is high your ph will also be high but this will drop when your Ammonia drops. How much depends on the water hardness of your water but thats a subject for later on. I'm sure Ammonia has a ph of 11 so you will see why your ph will be up during the early stages. Your Platties would be enough to cycle your tank if you return the rest of the fish to your LFS. Dont feel to bad about whats happened as it happens to most new fishkeepers and its the LFS thats at blame not you. The stocking level for a 10 Gallon tank would be 10" of fish if there is 10gallons of water in the tank but as you've got orniments, plants and gravel that also take up room the more realistic level is 8" of fish in a newly cycled tank of the size of your tank. IMO you should cycle your tank with 4 Danio's or three small Platties. Hth