The leopard Danio is actually the same species as the Zebra Danio, it is a variant developed I think in Europe. You can read more in our profile, click on the shaded fish name (like Zebra Danio) to see the profile.
This is an active fish and needs space and a good sized group. Six is considered absolute minimum, but 8 would be better. Provided you really like this fish, I would get more. You will then be pretty much at the limit of your 29g though. Sometimes stores will exchange fish for credit, if you decide you don't want more and can take the 3 back.