Neha, it was not the biggest mistake. I’m sure you feel bad, but you are trying. I killed all my fish when I moved many years ago, they froze as we drove across the state. Every single fish I had, they all died. That’s how I know moving tropical fish in winter is a stupid move. You, on the other hand, are trying to help fish, to learn, and to do better. Your best bet, is find another pet supply store. See if you can find one that does have knowledgeable people working there, who will help you. API is the brand most people here seem to recommend as the best, but it may not be carried there. So look for a solution test; where you add drops of a liquid solution to a small amount of your fishes water, wait for it to turn colors, and then match that on a color chart which will tell you the quantity of what’s in the water. The test kit should come with a solution for ammonia, nitrate, nitrite, water ph, glass tubes to test in, and the color chart. But, if you cannot find one, test strips are better than nothing.
Do not get discouraged, use this as a learning experience. You can learn about fish, and about how adults can argue but not be mean, nor give up on what they think. You are trying to do right for your fish, and that gives them a better chance than many others will have.