I just figured that the original source was created on 1440x900 a 16:10 monitor, and I am trying to render for 16:9. Can this be the fault? How do I go about it? Changing the pixel size helps, but it distorts the camera view.
The perspective camera works like a real camera lens, meaning that here will always be some degree of perspective distortion. As with real cameras, the best way to minimize it is to move the camera back and zoom in. The farther the camera is from the subject the flatter the projection will be.
Or you can use one of the non-perspective projections for your render camera (e.g. front, left, right, etc). Those cameras will give you perfectly undistorted results. The down side, of course, is that you can't orbit those camera views.