I always rip long pieces off for borders; I rip them about 2-1/2" wider than necessary and trim back down. That might not work with a print though (I'm usually using solids for borders). If you have some spare fabric I'd do a test rip and see how on-grain the print is. If it's off, I agree with the others, lay it out and use scissors on one layer at a time so you can get the print you need, then you might want to starch it before attaching since it's off-grain.