Don't you wish you could stand up and say "YOU SHALL NOT STEAL" just like Gandalf screams "You shall not pass". Hell, I would totally stand and scream it out loud if I had a cool staff like Gandalf.
The point is, if you are worried there are several tools available online using which you may check if your content is present on other websites. I found this tool online; feel free to take a look. I have not tested it extensively and so, I cannot vouch for it. Yet.
So, happy blogging. happy creative writing.