Early postoperative recovery
At 3 weeks postop, mild asymmetry or crookedness may be due to swelling. Alternatively, the cartilages in the nose have memory and even though maneuvers may have been performed to attempt to straighten the nose, the cartilages can try to recoil to their previous curvature causing residual crookedness of the nose. Applying digital pressure several times per day for several weeks to counteract these forces can help and it sounds like that is what your surgeon has instructed you to do. You should continue to follow your surgeon's instructions to get the best possible result following rhinoplasty.