It might be the good old "brick swordtail". I agree with Colin - it's a bit stretched out for a platy. The lines are fine, because a lot of the pet store fish are old hybrid forms dating back 50 years or more.
Looks exactly like our two-month-old Sword. My opinion does not mean much because I do not know much though, (but my learning curve is steady as she goes).
Was pretty sure it was a live bearer, but scud farming is kind of like aquatic composting, so could have been an egg on a plant somewhere that got added to the bin…