Here scribe 2 of π omitted the now when he copied the text from π into π. Oliver Cowdery later supplied it when he proofed π against π. The 1830 edition, set from π, also has the now; thus we can be confident that π also had the now. See under Helaman 7:29 for another instance where the scribe (in that case, Oliver Cowdery) omitted the original now after behold, at least initially, when he copied the text from π into π.
For this part of the text where both π and the 1830 edition are firsthand copies of π, I will usually not discuss those cases where the variation consists solely of a correction by Oliver Cowdery to scribe 2 of πβs reading (or scribe 2βs own correction), providing the corrected reading agrees with the 1830 reading. In volume 3, I list all these cases of manuscript variation between 3 Nephi 19:21 and Mormon 9:37, where scribe 2 of π was the main scribe in π and the 1830 edition was set from π; unfortunately, π is extant for only three minor fragments in this part of the text.
Summary: Maintain the now in 3 Nephi 20:10 (βbehold now I finish the commandmentβ), the 1830 reading and Oliver Cowderyβs corrected reading in π.