You said it's only be 3 days since you've had them, right?
They are probably still settling into their new home. Fish can take a few days, sometimes even a week or more, to settle in. (My sister adopted a betta recently, it took him 5 days before he was out and about in his 30 gallon planted tank and a week before he would come out to eat).
I've had groups of 6-8 before (in a 10-someone gave them to me as they had them in a 1 gallon tank, I definitely think a two foot tank is far too short for these active and zippy little fish, 29, and 55), and never had issues with them hiding.
I don't recall what size tank you said you had, but getting more would definitely help them feel safer too I bet. This is a very social fish species that lives in large groups in the wild.
Having lots of stuff for them to hide in to helps make them feel more secure, along with lots of ground cover such as driftwood or plants. Like the previous poster said, the more stuff you have for them to hide in, the more out and about they will be because they feel safe knowing they can dart into a safe hidey spot easily.
Maybe I've just lucked out with mine, as I would always see them zipping around during the day. They also would get especially zippy after a water change
Feeding frozen bloodworms too will usually lure them out
They slurp them up like spaghetti noodles!