@Chlotus If you don't feel comfortable with it, don't let others pressure you into doing it. If you originally did not want to do it, then I think you should stick to what you personally think you should do. If you change your mind about it and decide you want to post your art online, that's okay, too. Plus, I agree, you can never trust the internet, so I would advise you either don't post your art online, or post it online, but add a unique signature/watermark so people can't claim it as their own.
I feel like I'm rambling... did any of that make sense?