You're not suppose to choose finding the portal. Frodo didn't choose to have the Ring in the first place. He chose to go to Rivendell and get it away from the Shire. It's a two-part thing, right?

[What's that thing they talked about in English class? The hero circle, or whatever?]

There's the part you don't agree to, but then there's the choice. Imagine if Frodo said "no, I want to stay here" and Gandalf strapped Frodo to a wagon and used him as hot pad for the Ring. There's no way he would make it to Mount Doom if that's how his journey started, right? He had to make that first decision.