Sometimes, the print results cause a white line to appear near the magnetic stripes of a card.
It is usually due to the fact that the physical cards being used are somewhat different from the standard magnetic layout models in cardPresso.
However, it could also be caused by some printing offset issues from the driver of the target device.
Either way, you can always adjust the position and size of the stripes, within any cardPresso magnetic layout.
You can refer to the following document that explains how to do it.