Hang on to your IP, don't post it (look at the T&C of any site)...
Do THESE things:
1)
A) On ANY scrap of paper, in ANY file, etc., which contains ANY version, put this notice:
COPYRIGHT (C) <start year> - 2025 by <Full name>
<start year> is the first year you started it
<Full name> is your full, legal name
B) If there are ANY bits out there, try to edit them to include that or inform the owner of this; DOCUMENT DOING SO.
2) Make anyone who looks at it sign an NDA. This NDA should make the other person acknowledg
a) the story is your IP (Intellectual Property);
b) you have sole copyright in said IP;
c) that they do NOT have your consent to use it for ANY purpose whatsoever, including (but not limited to) creating their own work using ideas in your story;
d) ANY use of your IP for any purpose MUST be done by negotiating a license for such use with you, IF you wish to do so;
e) ANY violation of the NDA will automatically cost them $10,000 PER VIOLATION.
f) That they have received the amount of ______ as your consideration for this contract.
[You have to pay at least $1 to satisfy the legal notion of a "scintilla" of consideration to form a valid contract, but you should consider more for a stringent NDA and you should consult an IP lawyer.]