New Fuel Tank / Seal yet massive Leak after filling my Tank

Hey Guys, I finally took my 75 RestoMod for its first Gas Station "Filler Up Please" and discovered before starting the car to leave I had a massive leak from the Filler-Tube/Seal/Tank.

When placing the Seal it appeared to be doing the job correctly (Snug Fit), but now I'm at a loss.

Anyone have any experiences or recommendations before I spend my Saturday dealing with this annoying problem thats keeping me from discovering other issues I need to tackle! ;)

Thanks in advance !