Nice work, Sam! The only minor thing that caught my attention is that the first vareia on the first line should be removed.
In my experience, the final repetition of a Prokeimenon can differ slightly from the first and second repetitions. When this happens, the final repetition usually shares a similar melodic contour to the first and second repetitions but tends to employ variations of the same formulae which have more "finality" (for lack of a better term), as well as a "final cadence for Theotokia" (in the terminology of the formula book).
You could do compose a melody for the third repetition of this Prokeimenon as follows: For the phrase "The Lord will give strength unto his people," blend the first (100100) formula at the top of page 708 and the 10100010 formula on page 702. For the phrase "The Lord will bless his people with peace," you can use the 100010X formula on the top of page 720. (Even though that formula is usually accented on the third to last syllable, it is acceptable to use it with a phrase that is accented on the fourth to last syllable. In fact, at least one master composer did this, as is clear by looking at the 1001 formula on page 245).
If you follow this suggestion, it might be worth considering adjusting the melodic contour of your original composition so that the first and second repetitions match the melodic contour of the final repetition. You could do that as follows: For the phrase "The Lord will give strength until his people," blend the first 0100100 formula on page 708 with the third 010 formula on page 703.
In the end this is a purely creative suggestion, since the melody you composed is valid.
Basil