The 1858 Wright edition accidentally replaced the gerund prophesying with the plural count noun prophesyings. The probable source for this error is the immediately preceding verse, which occurs at the end of the previous chapter and has the plural sayings:
The 1908 RLDS edition removed this error from the RLDS text, probably by reference to the printer’s manuscript.
Normally in the Book of Mormon text, the complement of “make an end of” is a gerund (29 times):
speaking (20 occurrences in all, including the conjoined instance in Mosiah 25:14, cited below under reading)
prophesying
teaching
reading
praying
abridging
But the text also has nine examples where the complement is a plural count noun, with sayings occurring seven times (but there are no occurrences of prophesyings):
Finally, like the original text here in 2 Nephi 31:1, there are a few more cases of a possessive pronoun preceding a gerund-like noun:
For the third example (3 Nephi 5:19), it is possible that my saying is an error for my sayings, especially since my sayings occurs fairly often in the text, including nearby in 3 Nephi 10:19 and 3 Nephi 26:12. Of course, in 3 Nephi 5:19 the singular is in the following relative clause (“which is of myself ”) suggests that the singular my saying could be correct, although one could argue that singular is may have been the source for accidentally writing my saying instead of my sayings. For further discussion of this example and its possible emendation, see 3 Nephi 5:19.
Summary: Maintain in 2 Nephi 31:1 the gerundive noun prophesying in “I Nephi make an end of my prophesying unto you”.