What I'm thinking (may help, may be totally wrong):

It sounds like a generally good set-up. You did add the hatchets rather soon, the nitrate cycle takes about 3 weeks (it essentially does that each time you add fish).

That shouldn't be a horror, though! Hatchets are tetras and are a little sensitive to water quality. You might try a 5 or 10% water change (tomorrow should be fine - I don't know what time it is where you are). Make sure the water is at least the same temperature as the tank.

Were the fish at the surface in the store? You might wander by the fish store tomorrow (assuming it's too late tonight, again) and take a look at the tank you got them from. See if the fish are acting the same there. You might also ask how long the store has had them, if you don't know. If they came into the store less than a week before you brought them home, they might "just" be going through some extra stress.

Hopefully the other tetras are feeding. Sometimes hatchets will take a few days to settle in, and especially if wild caught or pond raised, flake food doesn't come naturally to them. Sometimes they settle in right away. Usually they'll settle in.

Watch the fish over the next day or so. See if they're pooping (if they are, they ARE eating, even if they don't seem to be eating). See if they're bellies get any hollower.

Hope that helps, even if there are some mixed messages in there. Welcome to the wonderful world of fish!