Fuel tank over full?

I finally got my car on the road this past week. I got gas last night (Tanks, inc EFI tank with aftermarket guage and sender) but the pump wouldn't stay on, so the attendant had to hold it. He asked me how many gallons I wanted.

Being that I haven't driven in 8 years, I said 12, due to the guage being close to E. Drove it home, parked it.

This morning, I wanted to take it work, but after I fired it up, I saw fuel dripping from the grommet the filler neck goes in. I then opened the cap and looked down the filler neck and fuel was cresting up the filler neck.

Did I put too much in? Or do I have a faulty grommet? I was going to siphon some out after work.

70 Dart, non vented cap, vented through filler neck.