The water line sags pretty bad in the middle. Is that because of the way the camera pivoted on the tripod? I was very careful with the placement of the tripod, I'm pretty sure it was level all the way across. .
Let's call what you refer to as the waterline, …"the shoreline".
You can not accurately portray the far shoreline as a straight line, if in fact the shore in the center is closer to you than at the sides.
A simple compositional correction, to give a more satisfying "balance" to the eye, would be to tilt the image so that the "chord" of the shoreline curve ( a straight line between the ends of what you call the waterline, i.e., the dark streak approximately midway up the image) is "level".
You will lose a bit of the left foreground shore, but the image will, IMO, "Feel" more "right".