Am I being over-paranoid?

Yes, almost certainly. Few ideas are really original. If it is something you can protect with a patent then you should speak to a patent attorney and ask any funders to sign a non-disclosure agreement (NDA). If the idea is like most and not unique, and does not have any protectable intellectual property then asking many funders to sign an NDA will probably appear naïve and put them off. They may well refuse to sign one anyway.

Remember most people are busy in their lives doing what they are already doing. There is always a small risk that someone may like your idea and run with it but the upside of talking to people about the idea is you get feedback and can improve the proposition. This will in turn increase the chances of getting financial backing. As soon as you launch people will know about your business, so you’re only delaying the inevitable.

See also: Using an NDA in your small business