When copying from 𝓞 to 𝓟, Oliver Cowdery initially wrote “promised land” instead of “land of promise”, but he immediately caught his error, crossed out the word land as well as the d of promised, then supralinearly inserted land of before promise (and all of this without any change in the level of ink flow).
Elsewhere the text is evenly divided in its use of “land of promise” versus “promised land” (21 to 21), so either reading is possible here in 1 Nephi 10:13. Of course, 𝓞 is extant and Oliver Cowdery corrected 𝓟 to agree with 𝓞.
Summary: Follow the earliest textual sources in choosing between “land of promise” and “promised land”; here in 1 Nephi 10:13, the earliest reading is “land of promise”.