I told some students about a plan I have for the future. I worry it could backfire long-term if we perhaps meet at a corporation for instance, perhaps after academy. As if confiding dooms me to be exploited, even if forgotten and appearing after a long time.

I want to take the plans. I read it makes it harder to take the plans when confiding them and it's true. But I can fight those feelings if I must.
However what concerns me as I mentioned, is its effects on competition on the long-term. How can I make sure to seal the "gateway" to me, so I'll be able to handle the competitions?

I'm not really sure how to answer your question. I'm not sure what you mean by exploited. But I have felt weird sometimes, after telling certain people my goals. Especially if it is something I really want, and the person who I told it to was either unencouraging, or dismissive. That being said, I have read that telling people and announcing your goals can make you lose momentum too. But I think it's a motivational thing, and I don't think it means it can't be done. If you run into them again and you're not there yet, it doesn't mean you never will be. Keep trying and working toward your goals.