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.