Gald you asked that question. Watched the video, but what if you are using a bigger cut of material? Or should I cut it down?

Do you mean longer yardage? If that is the case I do it on the floor or large table. Usually by the time you straighten the first yard or so the rest will follow. If not I pin a few pins than move along the fabric straightening another yard or so. If the fabric still doesn't fall into place than you have a really out of wack piece of fabric.