If there is no margin at the top, the booklet isn't the problem, it is the machine is misaligned, you cannot print past a quarter inch from the edge of the paper, it is supposed to be impossible (You can't do full bleed on Xerox devices), you should have a 4mm (1/4 inch) border all the way around.
Moving past that, there is no driver for the 250 that will work in Windows 10 properly, so either you are using CWS4, CWS5 and importing pdf to print, or printing with another driver, I would assume one from a 260 on Xerox.com that supports Windows 8, or a 250 from EFI.com
So part 1, you should be able to log into the 250 itself, and go to Machine Status > System Settings > System Settings > Common Settings > Maintenance > Adjust Image Position and maybe fix the shift that makes it go off the page where it shouldn't.
Most often, when the booklet sizes incorrectly, it means Imposition reduction failed, and this happens often with EFI products, they always assume you did it wrong, so when you create a doc as 8.5*11, it does not need to be resized at all to make a book on 11*17, but they do. Luckily, it is as simple as unchecking the box, seen here.
Or in a 260 driver here
