If you had it tested before you added fish what did you use to cycle the tank? If you did not have fish, or some other source of Ammonia, then your tank is probably not cycled. Just running an empty tank with the filter running will not cycle your tank.
Fish waste produces Ammonia, which is toxic to fish. Ammonia levels will continue to rise for a couple of days to a couple of weeks, it varies. After Ammonia has been present for a while bacteria develops that changes the Ammonia to Nitrite, which is also toxic to fish. The Ammonia levels will fall and the Nitrite levels rise. Eventually another form of bacteria will form that will transform the Nitrite to Nitrate, which is a much less toxic substance. Once you have gone through all of these steps and see Ammonia and Nitrite levels of zero and rising Nitrates the tank is cycled.
How long have you had the fish in the tank? You should have your water tested again to see if you have Ammonia. If you do have Ammonia and/or Nitrites you will have to perform frequent water changes to keep these levels below toxic.
If you have the lfs do another water test ask them for the actual numbers, not just if it passes or fails. When you get the numbers post them here.