You have not taken into account the Pixel Aspect Ratio - you have assumed the pixels are square, when for PAL they are not as it is grounded in CRT technology which used pixels wider than they are tall due to the way a CRT scans horizontally.
For example, PAL is 720x576 (4:3) with a PAR of 1.067
720/4*3 = 540
720/4*3 * 1.067 = 576.18 (Not sure about the .18, maybe I did the math wrong, but I am pretty sure this is your answer)
I think I recorded in 16:9, is it still possible to get this 720x576 resolution with that? Or did I do something wrong.
Anyhow, thanks for your reply!
If it was recorded in 16:9, no there is no way to change this to 4:3 without cropping, letterboxing or deforming the image (which will result in things being the wrong shape).
Cropping or letterboxing will be your best options. Probably cropping as you would still get full screen but you would lose a bit on the left and right. You could move the viewport around though if there was something in the cropped bit that needed to be seen.
Howver I would not do this - I would just render it out at 16:9. If it is viewed on a TV, it would likely just show ithe middle and chop off the edges or letterbox it, depending on the TV. (Think about what happens when you watch a film on a 4:3 TV that is broadcast widescreen)