If the wall is not holding back an earth load, it's not a retaining wall. It's a freestanding wall. You'll need a concrete footing, 8" depth (thickness,) whose base is below the frost line and whose width is double the combined width of all masonry that sits on it (block + stone.) You'll need rebar, embedded in the footing that continues to the top of the wall, every other block. The cells through which the rebar pass will be filled with concrete. Use truss or ladder mesh at every other course. While most of the illustrations and videos about building a cmu wall are for building structures, the principles are the same, so adapt for your needs.

to expand on what I said - there's no fixing this. This is built by someone lacking a fundamental understanding of how to build a cmu retaining wall. It WILL fail. Here's a detail drawing of how it should've been built, per a local county's typical wall guidelines. Whoever you hired is incapable of the work.

show a picture, including some surroundings. You'll need to leave an unfilled gap. But probably the better thing would be to disassemble a couple of sections of fence, construct the retaining wall and install the fence on top of it.

@3onthetree Thanks for understanding where the soil will be placed. I guess I took it for granted that people would imagine the mound placement, but I was wrong and I should have described it better. Eight inches of base would support a car driving over a paver. We really need that much material to support 100 pounds of blocks? The old style of base - still widely used - is to use sized gravel that goes down to fines, and then compact it. The newer method is called "open-graded base" and uses 3/4" crushed rock without any fines, and then above that 3/8" crushed rock without any fines. Believe it or not, this works fantastically well. It drains far better than material that includes fines. Technically, you are supposed to use a 3/4" base and then an additional layer of support fabric, then 3/8" crushed rock without fines as your bedding layer for pavers or stone blocks. If I were doing something with more serious weight, I have discovered that mixing 3/4" and 1/4" rock together and using that as the bottom of the base works as well or better, then you can put a 1/4" bedding layer on top of that without needing to lay extra fabric layers. https://www.youtube.com/watch?v=Ld4VCyHEHt8 In this case, we do not need to support a lot of weight, so I was hoping to "cheat" and just lay down fabric at the bottom of the ditch and then use however-many inches of 1/4" gravel as both the base and the bedding layer combined.