It looks okay to me, it does like you are off a little, but most tanks are. And I have seen a lot worse then that. You just don't have a frame around the top of the tank that would hide the filled line. Consider adding black tape, duct tape (2") around the top of your tank. This will not allow you to see whether your water is uneven or not, because the line will be above the tape. I think it will give your tank a more finished look as well.
Looks like a nice tank in the making!