Strongly sheared colloids often form strings oriented along the shear direction, which in turn often order into a quasi-2D hexagonal lattice. We examine this ordering process in detail to elucidate its strong system-size dependence, which is a major obstacle to establishing a connection between simulation and experiment. We catalog the possible lattices and use an energy criterion to predict which one a particular system is likely to crystallize in. The process is similar to nucleation and growth in a true 2D system except that strings crystallize without point defects (vacancies and interstitials), unlike 2D disks, because particle (string) number is not conserved.