What does Huck mean when he says, "it was a close place... I was trembling, because i'd got to decide, betwixt two things, and i knowed it." What "two things" does Huck have to decide between?

Those two things were turning Jim in and being a hero..... doing what he believed to be the proper, lawful thing..... or staying with Jim, protecting him, being his friend, and going to hell..... Huck chose Jim's friendship and hell.

It was a close place. I took it up, and held it in my hand. I was a trembling, because I'd got to decide, forever, betwixt two things, and I knowed it. I studied a minute, sort of holding my breath, and then says to myself:
"All right, then, I'll go to hell"- and tore it up.