Fuel Gauge Question

So ever since I reassembled my Dart, which included a new fuel tank, lines and sending unit (everything in the fuel system), the fuel gauge only reads 3/4 full when I have filled the tank all the way up (nearly to overflowing). My question is, when the gauge is down almost to "Empty (E)" (I have not passed the E line yet) and I fill it up, it only takes 9-10 gallons. So I am safe to keep driving for awhile even after it hits E since the car presumably still has 8-9 gallons in the tank, or am I risking running out of fuel (or at least reaching a point where it does not pick up any more fuel)? Would appreciate any thoughts you guys might have on the subject.