Hello Vanquyet,
Yes, 3km is perfectly feasible with LoRa. Just note though that connecting peer-2-peer between two end-nodes is not LoRaWAN, which by definition is based on a gateway/server network structure. You would have to set up your nodes to use LoRa modulation and then create your own P2P protocol to use instead of LoRaWAN.
Alternatively, if you want to take advantage of LoRaWAN standard (which is worthwhile because it is a well built and robust protocol) then you'll need to get your hands on a gateway and connect it through to TTN servers. You'll build a much better system that way.
Good luck!
JDP