Tam Lin translation exercise

I don't usually post translation exercises, or take part in them, but I've
been listening to Fairport Convention's version of "Tam Lin" recently, and
one verse in particular is going through my head, and I thought it would be
fun for everyone to play with. For those who don't know the ballad, Tam has
told his lover Janet how he came to be stolen away by the Queen of the
Faries, and before going on to tell her what she must do to rescue him, he
explains why he needs to be rescued tonight-

"But at the end of seven years
We pay a tithe to Hell;
And since I am so fair and full of flesh,
I fear 'twill be mysel'."

Pete