Welcome to Tropical Fish Keeping forum.:-Di went to petsmart n got my mollies n the dude there picked my tank out n said that was a good size for them n it came with the filter n heater n they check my water n all they say it is good n the reason why i cant get a bigger tank if really none of ur business jus want to know what i can do with it till i can get a bigger tank
I'm sorry your first experiences are so negative, but everyone here cares passionately for the well-being of fish. So we want all fish, including yours, to be at their best. They are after all living creatures and they need certain things to live a normal healthy life.
Sadly many pet stores have staff with little or no experience. There are exceptions, even among the "chain" stores, but not everywhere. There was a time when beginning hobbyists had no one but the store to ask for advice, and many of us lost fish after fish. Now days we have the internet with forums like TFK. Always, always find out from those who know first, before buying fish , tanks, etc. Not only will the fish be better for it, but you will save money too.
As others have said, a 1.6 gallon tank is no where near sufficient space for any fish [except a Betta]. I would return the fish. Or buy a new larger tank. And if you are going to do the latter, you want a 20 gallon tank, preferably what is called a 20g long, which is 30 inches in length and holds 20 gallons. You can have slightly more fish in a longer tank. The Common Molly needs this space, it will grow (if it is healthy and survives). Read more in our profile, click on the shaded name.