The only Graptemys species naturally occuring there are the Sabine Map Turtle(Graptemys ouachitensis sabinensis), and the Mississippi Map Turtle(Graptemys pseudogeographica kohni). It is theoretically possible that you have an escapee, but very unlikely. Most Map turtles are restricted to one major drainage system.
:i caught it on lake toledo bend on the border of texas and louisianna. back in a creek. to me he looks more like the barbour's map but i cant tell for sure right now it hasnt shed it's shell yet.