I dont see how you can see a white dot in that photo...
Anyway... Im going to take a guess and say thats a Double Tail HalfMoon Plakat female.
Here's you normal DT Female: Notice the shorter dorsal fine like dr2b mentioned.
And here's a DT Female Plakat:
The dorsal and anal fin look to be the same size, which is a major trait to Plakat's. Males also have very long ventral fins, females tend to have ones that are much shorter.
If it is the female plakat, I think you got a very good deal on a $12 fish lol.