The needle should be mid scale at that resistance BUT "is the resistance" actually appearing at the gauge stud?
The path is engine block and ground, sender, sender wire end terminal..........through the bulkhead connector terminal............to the cluster harness connector.........the pc board pin.........to the pc board trace.........to the gauge stud and nut. Any of those points could be a poor connection, OR the gauge wrong, or not getting proper power from "the other end" of the loop.
If you are sure you are correct in your measurements, and can check it clear back to the gauge, then I'd eliminate the sender and sender wiring.
This is why I often talk about "thinking of it as an end to end system" (instead of one or two parts) and think/ draw/ keep in mind the "circuit path"
