A 4 gallon tank is IMO too small to house a school of neon tetras.
Also since in you're located in India, I wouldn't be surprised if the fish you purchased are harvested from wild sources. Hence..... making them even more skittish than the tetras we have available in the states that are raised in fish farms.
Other than that, your nano tank looks nice with the plants/substrate.
If you had a 20G tank to put a school of 10 neons, plants & no predators, you would notice a HUGE difference in their behavior.