Corners are never square, and pretending otherwise ruins the wall
At the corner
Cut the length so about fifteen millimetres turns the corner. Start the next length plumb on the new wall, overlapping that turn.
Re-plumb every wall
Hang a plumb line on each wall rather than trusting the previous one. Four walls of a room are rarely within ten millimetres of each other.
Pattern matching
The pattern will not match across the overlap and cannot be made to. Put that corner where it is least visible from the door.
