The square flange is correct. The filler tube goes from the outside in. There should be a rubber boot over the filler tube and pad with the gas door bumper between the flange and body. At the tank end you should have an offset rubber hose 3"-4" long (fuel rated) between the tank and filler tube. The outside square flange is attached to the body with 4 screws and there should be another square metal support flange at the bottom of the filler tube rubber to fasten it to the trunk floor. Just did mine last weekend. Filler tube went fine, wish the metal cover inside the trunk would have fit as good.
