Congratulations on your fish! They are very pretty, and those are my favorite kind of platies.
I am afraid there is a problem, though.
I hope I am wrong, but it does not look like your tank has been cycled. You said you waited a week before putting in your fish....why?
If the aquarium store told you that running the tank empty for a week would cycle it, they gave you bad advice. Running the tank empty does not cycle it. Your tank needs to be cycled for the safety of your fish.
If your tank was not cycled using another method, your fish are at risk of dying soon. They pee ammonia, and it will burn their gills and kill them. During the first six weeks they are in the tank, you will need to change some (but not all) of the water in your tank every few days, so the ammonia does not build up too much. During the first six weeks, your tank and filter will grow a colony of good bacteria that turn the ammonia in fish urine into something less harmful to them (ammonia to nitrite to nitrate). After the cycle is complete (your bacteria are grown), you will not have to change the water so frequently.
The other option is to return your fish now and do a fishless cycle before adding fish. For a fishless cycle, you will have to dose ammonia in the tank, or use raw shrimp to get a cycle going, but you won't have to do water changes. That will mean less work for you, and your fish will be safer. However, you will have an empty tank for a while.
Please read about cycling, or your fish will likely die in the next couple of weeks. You will need a water test kit that includes tests for ammonia, nitrite, and nitrate. If your fish stay in the tank, you will need to change some of the water every time ammonia or nitrite levels rise above 1.0. As long as you keep levels below 1.0 (preferably below 0.5), your fish can survive the cycle in your tank. You will know the cycle is over when your nitrites and ammonia fall to zero, and your nitrates rise. It will take about six weeks. During the cycle, do not change all the water at once. Also, do not clean the filter, and don't clean the gravel too much. You are growing the good bacteria in those places. Make sure you use a good dechlorinator and match the water temperature with every partial water change.
Please keep posting here and asking questions! There are lots of people here who had the same problem starting out, because fish stores gave bad advice. Your fish are lucky to have someone who cares about them. People here will help you through the cycle if you keep posting!
Good luck!