Filler neck on 35 ford not tight enough

[JJOHN]

I just removed my filler pipe on my 1935 ford and replaced the lead washer at the base of the pipe. When I tighen it up, I can't seem to get it tight enough so that the filler pipe does not rotate-reason for the leak I believe. I have a spanner wrench to tighten the collar but am afraid to really crank it down. Should I add another washer or some other thing to take up the space.