How to scan your body in 3d?
With sufficient practice one can develop the ability to very quickly and accurately observe several points in the body in very quick succession.

In a single mind moment only one point in the body is observed, however since mind moments are so fleetingly small, with good concentration intermediate meditators can pass attention to several points in quick succession such that it can appear as a single observation.

With good concentration one can pass the attention from top-down in a ray trace fashion, or left-right, and observe all points in between.

There is no reason to be in a hurry, or be impatient - the quality of meditation does not depend on the number of times the body scanned, but on the quality of the observation. If it takes a lot of time to go inch by inch, that is valuable practice too, since it develops patience and perseverance.