Whenever I feel I might be railroading players, it's because I haven't worked on the backstory enough. A world should be larger than the vista presented to the PC's. Should they walk to the horizon, something will be waiting for them, rather than the edge of the world. The intrigue of the island, the political factions, and the monsters stuff usually comes easy. What's hard is keeping the PC's interested in a geographically narrow storyline. If you're creating a lost continent campaign, here's some things to consider:
1) How hard is it to travel to and from? If the continent can be found easily, then PC's could just say, "f-this! Let's go someplace else." There should be a solid explaination why it's
lost. This is the most important piece of information to consider. Maybe the lost colony isn't lost at all. Maybe there's sea monsters that wreck the ships so no one can leave the island. The colony is still there but they've lost contact because no one can leave the island continent. Whatever you come up with, it should be important, believable, and harrowing. Make sure staying on the island continent is the
safe bet. Tell the PC's they're the 3rd expedition. When they arrive, have the colonists say, "You're the first of our people we've seen since the day we left home."
2) Conflicting stories adds intrigue. One thing I learned as a DM is telling the truth can be quite boring for players. It's better to have some people exaggerate. Others leave out vital information. While still others down play serious dangers with skepticism. It keeps the PC's from asking just anyone and adds a touch of character to the bumpkins. Also, when you can't trust the only sources of information available it forces the PC's to look and judge with their own eyes. If the colonists say there's a group of demonic ogres that controls the forests and the characters find out it's ettins, that changes everything. Information given should be ballpark accurate, but it's up to the PC's to get the details.
3) Diminishing Supplies. Ban any items that create food and water, and cure diseases/poisons on a daily basis. The problem with these items is they destroy necessary conflict (and they're just bad for "stranded" storylines). By removing the fast-food industry from your island (I just got an image of Joe vs the Volcano) you're creating more story options. An example might be - the town is low on food and fresh water. The river valley two miles east is lush with game and fruits, only it's a treacherous hike through the forests and a dangerous climb down. This gives you the opportunity to have the PC's fight for survival. I recently finished a D&D campaign where our group was trapped in the Underdark for 11 levels. For the first 7 levels we ran out of food. Literally, we would chase down wandering monsters to kill and eat them. It is some of the best Roleplaying we've ever had. But I must admit, Drow is an acquired taste
