Ah, well you need to improve on that a bit
What you did is like going from the US east coast to west coast with a truck and transporting just 25 kg of goods...
Fuel does not take into account the mass you carry, just distance and WHG modules installed / processing power.
So you need to upgrade the cargo bay and transport a lot more at once, and jump from one SoS to the other or multiple SoS before you have to get back to Earth.
You could even mix it with a combat mission that does "Pirate's nest" to loot pirate stations, then sell the stuff to SoS signals with your merchant / cargo ship. Ofc for that you'll need a combat ship in addition to the hauler.