All I can say is what I'd do and a couple of thoughts come to mind, assuming you're not keen to spend a lot more money. If you have enough $ to buy blocks intended for a retaining wall, I would do that, but otherwise, here's something that should work OK with what you've already got. Blocks intended for a retaining wall have a lip at the back or a key in the middle that stops them from slipping horizontally and yours don't have that.
If you backfill between the blocks and your pool, you're countersinking the pool. The pool manufacturer may or may not allow this with respect to your warranty. I'll bet not, so based on that assumption, would you consider moving the blocks much closer to the pool? (like maybe an inch or two away) If so, here's what I'd do. To build a retaining wall, you need some room behind the blocks as you build it. First off, the bottom course of blocks needs to be countersunk into the ground. Half the height of the block would be enough. So get the blocks out of the way and then dig down so you can make a nice level bed of gravel under the bottom course and about 3" down from the current ground level. Use a rubber mallet to set the blocks all to same height and level. Backfill and compact to the original level to keep those blocks in place. That wall is pretty low - looks like maybe 12" or 18"? I think for that low of a wall, adhesive would work fine. Buy good stuff and be warned it's not cheap because you'll need a fair bit of it and you don't want to skimp on it. Follow the directions on the tube to the letter. Let the adhesive set before anything else. Behind the wall, put some perforated ag pipe with an outlet somewhere on the low side. If you can get it, buy the kind with a sock over it. Cover the ag pipe with drain rock maybe 4" to 6". Put some landscape cloth over the drain rock, then backfill with top soil for the lawn to grow into, or top it off with turf. Those aren't the right type of blocks for a retaining wall, so essentially you're building something more like a dry stack natural stone wall. Therefore, it would be a good idea to tip the wall out of vertical slightly, by setting the second and third courses back into the lawn a little away from the pool, maybe 1/2" back for each course of blocks.
You could make it more solid by cutting some 3-foot long pieces of 1" wide galvanized strapping. Glue these pointed back toward the lawn between the top course and second course down, around about every 4 blocks or so. When backfilling behind the blocks, twist and then bend them at a right angle up against the original ground, so that they're tied into the backfill. You said it's not been getting any erosion, so this might be overkill, but it's pretty easy to do.
A good thing you have going for you, is that the shape created by your blocks is an arch so movement is restricted as long as the blocks are touching, end to end.
It's not quite kosher, but I think it would last a really long time. I haven't seen those particular blocks before, but if you know what they're called, the manufacturers often have websites with building advice. There may be mortared options if you don't mind doing some bricklaying. If that's possible for those, it would be sturdier and you could put some no. 3 rebar into the mortar poking out into the backfill. It's hard putting this all into words! Have fun with the project.
