As explained under Helaman 14:20, there are examples in the original text of both “all the face of the land” (24 times) and “the face of all the land” (2 times). There is also one instance of “the face of the whole land” (in Mormon 1:13). One of the two instances of the “the face of all the land” occurred originally here in 3 Nephi 8:20. The other one is found in Helaman 11:21: “and the church did spread throughout the face of all the land”. In the 1837 edition, this second instance of the less frequent phraseology (here in 3 Nephi 8:20) was replaced with the more frequent one, “all the face of the land”. This change was probably unintentional since the original phraseology does work and the change was not marked by Joseph Smith in his editing of 𝓟 for the 1837 edition. The critical text will restore the earlier reading, “the face of all the land”.
Summary: Restore the original word order in 3 Nephi 8:20: “the face of all the land”; there is evidence for this phraseology elsewhere in the text.