I wouldn't worry. First, I would think it virtually impossible to plagerize from a piece made public with your name on it. You have thousands of witnesses and a date stamped copy on-line.
Second, it is only an exceprt. Only you know where it's going.
The benefit of comment from other writers outweighs an almost nonexistent risk of having your work stolen.
I hope to see some of your work. All the best - Craven